diff --git a/Cargo.lock b/Cargo.lock
index 74db0ea4d7f..2dfb7f484a9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -921,9 +921,9 @@ checksum = "a26ae43d7bcc3b814de94796a5e736d4029efb0ee900c12e2d54c993ad1a1e07"
 
 [[package]]
 name = "elsa"
-version = "1.9.0"
+version = "1.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "714f766f3556b44e7e4776ad133fcc3445a489517c25c704ace411bb14790194"
+checksum = "d98e71ae4df57d214182a2e5cb90230c0192c6ddfcaa05c36453d46a54713e10"
 dependencies = [
  "stable_deref_trait",
 ]
diff --git a/provider/core/src/datagen/iter.rs b/provider/core/src/datagen/iter.rs
index 6175d89c6f4..ad6bc1b219d 100644
--- a/provider/core/src/datagen/iter.rs
+++ b/provider/core/src/datagen/iter.rs
@@ -22,6 +22,10 @@ pub trait IterableDynamicDataProvider<M: DataMarker>: DynamicDataProvider<M> {
 pub trait IterableDataProvider<M: KeyedDataMarker>: DataProvider<M> {
     /// Returns a list of [`DataLocale`].
     fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError>;
+    /// Returns whether a [`DataLocale`] is in the supported locales list.
+    fn supports_locale(&self, locale: &DataLocale) -> Result<bool, DataError> {
+        self.supported_locales().map(|v| v.contains(locale))
+    }
 }
 
 impl<M, P> IterableDynamicDataProvider<M> for Box<P>
diff --git a/provider/datagen/Cargo.toml b/provider/datagen/Cargo.toml
index 9599311bfd5..5f1177232cd 100644
--- a/provider/datagen/Cargo.toml
+++ b/provider/datagen/Cargo.toml
@@ -73,7 +73,7 @@ proc-macro2 = {version = "1", optional = true }
 
 # Other external dependencies
 displaydoc = { version = "0.2.3", default-features = false }
-elsa = "1.9"
+elsa = "1.10"
 itertools = "0.10"
 log = "0.4"
 memchr = "2.5.0"
diff --git a/provider/datagen/src/provider.rs b/provider/datagen/src/provider.rs
index ad9a2fbcd5a..fdfc914ba5e 100644
--- a/provider/datagen/src/provider.rs
+++ b/provider/datagen/src/provider.rs
@@ -7,7 +7,10 @@
 use crate::source::*;
 use crate::transform::cldr::source::CldrCache;
 use crate::{CollationHanDatabase, CoverageLevel};
+use elsa::sync::FrozenMap;
+use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
+use std::collections::HashSet;
 use std::fmt::Debug;
 use std::path::PathBuf;
 use std::sync::Arc;
@@ -78,6 +81,7 @@ impl DatagenProvider {
                 icuexport_dictionary_fallback: None,
                 #[cfg(feature = "legacy_api")]
                 collations: Default::default(),
+                supported_locales_cache: Default::default(),
             },
         }
     }
@@ -258,6 +262,24 @@ impl DatagenProvider {
     ) -> Result<impl IntoIterator<Item = icu_locid::LanguageIdentifier>, DataError> {
         self.cldr()?.locales(levels)
     }
+
+    pub(crate) fn supported_locales_set<M>(&self) -> Result<&HashSet<DataLocale>, DataError>
+    where
+        M: KeyedDataMarker,
+        Self: IterableDataProviderInternal<M>,
+    {
+        #[allow(deprecated)] // SourceData
+        self.source
+            .supported_locales_cache
+            .insert_with(M::KEY, || {
+                Box::new(
+                    self.supported_locales_impl()
+                        .map(|v| v.into_iter().collect()),
+                )
+            })
+            .as_ref()
+            .map_err(|e| *e)
+    }
 }
 
 /// Specifies the trie type to use.
@@ -306,6 +328,9 @@ pub struct SourceData {
     pub(crate) icuexport_dictionary_fallback: Option<Arc<SerdeCache>>,
     #[cfg(feature = "legacy_api")]
     pub(crate) collations: Vec<String>,
+    #[allow(clippy::type_complexity)] // not as complex as it appears
+    pub(crate) supported_locales_cache:
+        Arc<FrozenMap<DataKey, Box<Result<HashSet<DataLocale>, DataError>>>>,
 }
 
 #[cfg(feature = "legacy_api")]
@@ -485,3 +510,21 @@ impl SourceData {
             .locales(levels.iter().copied())
     }
 }
+
+pub(crate) trait IterableDataProviderInternal<M: KeyedDataMarker>: DataProvider<M> {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError>;
+}
+
+impl<M: KeyedDataMarker> IterableDataProvider<M> for DatagenProvider
+where
+    DatagenProvider: IterableDataProviderInternal<M>,
+{
+    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+        self.supported_locales_set()
+            .map(|v| v.iter().cloned().collect())
+    }
+
+    fn supports_locale(&self, locale: &DataLocale) -> Result<bool, DataError> {
+        self.supported_locales_set().map(|v| v.contains(locale))
+    }
+}
diff --git a/provider/datagen/src/transform/cldr/characters/mod.rs b/provider/datagen/src/transform/cldr/characters/mod.rs
index 68ea8b7e948..26cd1ee37df 100644
--- a/provider/datagen/src/transform/cldr/characters/mod.rs
+++ b/provider/datagen/src/transform/cldr/characters/mod.rs
@@ -5,10 +5,10 @@
 use std::collections::HashSet;
 use std::marker::PhantomData;
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use icu_collections::codepointinvliststringlist::CodePointInversionListAndStringList;
 use icu_properties::provider::*;
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use itertools::Itertools;
 
@@ -46,8 +46,8 @@ macro_rules! exemplar_chars_impls {
             }
         }
 
-        impl IterableDataProvider<$data_marker_name> for crate::DatagenProvider {
-            fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+        impl IterableDataProviderInternal<$data_marker_name> for crate::DatagenProvider {
+            fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
                 Ok(self
                     .cldr()?
                     .misc()
diff --git a/provider/datagen/src/transform/cldr/currency/mod.rs b/provider/datagen/src/transform/cldr/currency/mod.rs
index 9157f91a1bd..bd8dc3f35fe 100644
--- a/provider/datagen/src/transform/cldr/currency/mod.rs
+++ b/provider/datagen/src/transform/cldr/currency/mod.rs
@@ -10,10 +10,10 @@ use tinystr::UnvalidatedTinyAsciiStr;
 use zerovec::VarZeroVec;
 use zerovec::ZeroMap;
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use crate::DatagenProvider;
 use icu_dimension::provider::*;
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use std::collections::BTreeMap;
 use std::collections::HashMap;
@@ -95,8 +95,8 @@ impl DataProvider<CurrencyEssentialsV1Marker> for crate::DatagenProvider {
     }
 }
 
-impl IterableDataProvider<CurrencyEssentialsV1Marker> for crate::DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<CurrencyEssentialsV1Marker> for crate::DatagenProvider {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         Ok(self
             .cldr()?
             .numbers()
diff --git a/provider/datagen/src/transform/cldr/datetime/mod.rs b/provider/datagen/src/transform/cldr/datetime/mod.rs
index d0c28126adf..097ac024d33 100644
--- a/provider/datagen/src/transform/cldr/datetime/mod.rs
+++ b/provider/datagen/src/transform/cldr/datetime/mod.rs
@@ -2,13 +2,13 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use icu_datetime::provider::calendar::*;
 use icu_locid::{
     extensions::unicode::{key, value},
     Locale,
 };
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use once_cell::sync::OnceCell;
 use std::collections::HashMap;
@@ -207,8 +207,8 @@ macro_rules! impl_data_provider {
             }
         }
 
-        impl IterableDataProvider<$marker> for crate::DatagenProvider {
-            fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+        impl IterableDataProviderInternal<$marker> for crate::DatagenProvider {
+            fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
                 let mut r = Vec::new();
                 if DateSkeletonPatternsV1Marker::KEY == $marker::KEY {
                     for (cal_value, cldr_cal) in supported_cals() {
diff --git a/provider/datagen/src/transform/cldr/datetime/neo.rs b/provider/datagen/src/transform/cldr/datetime/neo.rs
index 3b861f5b12c..fee69df6ddd 100644
--- a/provider/datagen/src/transform/cldr/datetime/neo.rs
+++ b/provider/datagen/src/transform/cldr/datetime/neo.rs
@@ -3,6 +3,7 @@
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
 use super::supported_cals;
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde::ca;
 use crate::DatagenProvider;
 use icu_datetime::pattern::{self, CoarseHourCycle};
@@ -681,8 +682,8 @@ impl DataProvider<TimePatternV1Marker> for DatagenProvider {
 // subtag actually should be produced (by returning a special error), then this code is no longer necessary
 // and we can use a union of the H12/H24 key lengths arrays, instead checking for preferred hc
 // in timepattern_convert
-impl IterableDataProvider<TimePatternV1Marker> for DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<TimePatternV1Marker> for DatagenProvider {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         let calendar = value!("gregory");
         let mut r = Vec::new();
 
@@ -727,8 +728,8 @@ macro_rules! impl_symbols_datagen {
             }
         }
 
-        impl IterableDataProvider<$marker> for DatagenProvider {
-            fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+        impl IterableDataProviderInternal<$marker> for DatagenProvider {
+            fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
                 self.supported_locales_neo(value!($calendar), $lengths)
             }
         }
@@ -743,8 +744,8 @@ macro_rules! impl_pattern_datagen {
             }
         }
 
-        impl IterableDataProvider<$marker> for DatagenProvider {
-            fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+        impl IterableDataProviderInternal<$marker> for DatagenProvider {
+            fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
                 self.supported_locales_neo(value!($calendar), $lengths)
             }
         }
diff --git a/provider/datagen/src/transform/cldr/datetime/week_data.rs b/provider/datagen/src/transform/cldr/datetime/week_data.rs
index a4e47565c0d..cd3bbeec098 100644
--- a/provider/datagen/src/transform/cldr/datetime/week_data.rs
+++ b/provider/datagen/src/transform/cldr/datetime/week_data.rs
@@ -2,18 +2,18 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde::{
     self,
     week_data::{Territory, DEFAULT_TERRITORY},
 };
 use icu_calendar::provider::{WeekDataV1, WeekDataV1Marker};
 use icu_locid::LanguageIdentifier;
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use std::collections::HashSet;
 
-impl IterableDataProvider<WeekDataV1Marker> for crate::DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<WeekDataV1Marker> for crate::DatagenProvider {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         let week_data: &cldr_serde::week_data::Resource = self
             .cldr()?
             .core()
diff --git a/provider/datagen/src/transform/cldr/decimal/compact.rs b/provider/datagen/src/transform/cldr/decimal/compact.rs
index 1d7c40a5ffc..393af1e8ca9 100644
--- a/provider/datagen/src/transform/cldr/decimal/compact.rs
+++ b/provider/datagen/src/transform/cldr/decimal/compact.rs
@@ -2,10 +2,10 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use icu_compactdecimal::provider::*;
 use icu_locid::extensions::unicode::key;
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use std::convert::TryFrom;
 
@@ -105,14 +105,16 @@ impl DataProvider<LongCompactDecimalFormatDataV1Marker> for crate::DatagenProvid
     }
 }
 
-impl IterableDataProvider<ShortCompactDecimalFormatDataV1Marker> for crate::DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<ShortCompactDecimalFormatDataV1Marker>
+    for crate::DatagenProvider
+{
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         self.supported_locales()
     }
 }
 
-impl IterableDataProvider<LongCompactDecimalFormatDataV1Marker> for crate::DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<LongCompactDecimalFormatDataV1Marker> for crate::DatagenProvider {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         self.supported_locales()
     }
 }
diff --git a/provider/datagen/src/transform/cldr/decimal/symbols.rs b/provider/datagen/src/transform/cldr/decimal/symbols.rs
index 0bc72ed632b..a5f2de3b7fb 100644
--- a/provider/datagen/src/transform/cldr/decimal/symbols.rs
+++ b/provider/datagen/src/transform/cldr/decimal/symbols.rs
@@ -2,10 +2,10 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use icu_decimal::provider::*;
 use icu_locid::extensions::unicode::key;
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use std::borrow::Cow;
 use std::convert::TryFrom;
@@ -47,8 +47,8 @@ impl DataProvider<DecimalSymbolsV1Marker> for crate::DatagenProvider {
     }
 }
 
-impl IterableDataProvider<DecimalSymbolsV1Marker> for crate::DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<DecimalSymbolsV1Marker> for crate::DatagenProvider {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         self.supported_locales()
     }
 }
diff --git a/provider/datagen/src/transform/cldr/displaynames/language.rs b/provider/datagen/src/transform/cldr/displaynames/language.rs
index 8dad1d068e5..cfb9e680db2 100644
--- a/provider/datagen/src/transform/cldr/displaynames/language.rs
+++ b/provider/datagen/src/transform/cldr/displaynames/language.rs
@@ -2,11 +2,11 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use core::convert::TryFrom;
 use icu_displaynames::provider::*;
 use icu_locid::subtags::Language;
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use std::collections::BTreeMap;
 use zerovec::ule::UnvalidatedStr;
@@ -58,8 +58,8 @@ impl DataProvider<LocaleDisplayNamesV1Marker> for crate::DatagenProvider {
     }
 }
 
-impl IterableDataProvider<LanguageDisplayNamesV1Marker> for crate::DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<LanguageDisplayNamesV1Marker> for crate::DatagenProvider {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         Ok(self
             .cldr()?
             .displaynames()
@@ -77,8 +77,8 @@ impl IterableDataProvider<LanguageDisplayNamesV1Marker> for crate::DatagenProvid
     }
 }
 
-impl IterableDataProvider<LocaleDisplayNamesV1Marker> for crate::DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<LocaleDisplayNamesV1Marker> for crate::DatagenProvider {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         Ok(self
             .cldr()?
             .displaynames()
diff --git a/provider/datagen/src/transform/cldr/displaynames/region.rs b/provider/datagen/src/transform/cldr/displaynames/region.rs
index 4927e295605..c7bbdea7ed3 100644
--- a/provider/datagen/src/transform/cldr/displaynames/region.rs
+++ b/provider/datagen/src/transform/cldr/displaynames/region.rs
@@ -2,11 +2,11 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use core::convert::TryFrom;
 use icu_displaynames::provider::*;
 use icu_locid::subtags::Region;
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use std::collections::BTreeMap;
 use std::str::FromStr;
@@ -35,8 +35,8 @@ impl DataProvider<RegionDisplayNamesV1Marker> for crate::DatagenProvider {
     }
 }
 
-impl IterableDataProvider<RegionDisplayNamesV1Marker> for crate::DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<RegionDisplayNamesV1Marker> for crate::DatagenProvider {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         Ok(self
             .cldr()?
             .displaynames()
diff --git a/provider/datagen/src/transform/cldr/displaynames/script.rs b/provider/datagen/src/transform/cldr/displaynames/script.rs
index 354f206fd1d..0d347b34008 100644
--- a/provider/datagen/src/transform/cldr/displaynames/script.rs
+++ b/provider/datagen/src/transform/cldr/displaynames/script.rs
@@ -2,11 +2,11 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use core::convert::TryFrom;
 use icu_displaynames::provider::*;
 use icu_locid::{subtags::Script, ParserError};
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use std::collections::BTreeMap;
 use std::str::FromStr;
@@ -35,8 +35,8 @@ impl DataProvider<ScriptDisplayNamesV1Marker> for crate::DatagenProvider {
     }
 }
 
-impl IterableDataProvider<ScriptDisplayNamesV1Marker> for crate::DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<ScriptDisplayNamesV1Marker> for crate::DatagenProvider {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         Ok(self
             .cldr()?
             .displaynames()
diff --git a/provider/datagen/src/transform/cldr/displaynames/variant.rs b/provider/datagen/src/transform/cldr/displaynames/variant.rs
index 1adf22ae210..be788f09630 100644
--- a/provider/datagen/src/transform/cldr/displaynames/variant.rs
+++ b/provider/datagen/src/transform/cldr/displaynames/variant.rs
@@ -2,11 +2,11 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use core::convert::TryFrom;
 use icu_displaynames::provider::*;
 use icu_locid::{subtags::Variant, ParserError};
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use std::collections::BTreeMap;
 use std::str::FromStr;
@@ -35,8 +35,8 @@ impl DataProvider<VariantDisplayNamesV1Marker> for crate::DatagenProvider {
     }
 }
 
-impl IterableDataProvider<VariantDisplayNamesV1Marker> for crate::DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<VariantDisplayNamesV1Marker> for crate::DatagenProvider {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         Ok(self
             .cldr()?
             .displaynames()
diff --git a/provider/datagen/src/transform/cldr/list/mod.rs b/provider/datagen/src/transform/cldr/list/mod.rs
index baf184b9971..1ffd75d0430 100644
--- a/provider/datagen/src/transform/cldr/list/mod.rs
+++ b/provider/datagen/src/transform/cldr/list/mod.rs
@@ -2,10 +2,10 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use icu_list::provider::*;
 use icu_locid::subtags::language;
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use once_cell::sync::OnceCell;
 use std::borrow::Cow;
@@ -125,8 +125,8 @@ macro_rules! implement {
             }
         }
 
-        impl IterableDataProvider<$marker> for crate::DatagenProvider {
-            fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+        impl IterableDataProviderInternal<$marker> for crate::DatagenProvider {
+            fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
                 Ok(self
                     .cldr()?
                     .misc()
diff --git a/provider/datagen/src/transform/cldr/plurals/mod.rs b/provider/datagen/src/transform/cldr/plurals/mod.rs
index e10118cd814..79c1cbe71d6 100644
--- a/provider/datagen/src/transform/cldr/plurals/mod.rs
+++ b/provider/datagen/src/transform/cldr/plurals/mod.rs
@@ -4,10 +4,10 @@
 
 use std::collections::BTreeMap;
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use icu_plurals::rules::runtime::ast::Rule;
 use icu_plurals::{provider::*, PluralCategory};
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use zerovec::ZeroMap;
 
@@ -62,8 +62,8 @@ macro_rules! implement {
             }
         }
 
-        impl IterableDataProvider<$marker> for crate::DatagenProvider {
-            fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+        impl IterableDataProviderInternal<$marker> for crate::DatagenProvider {
+            fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
                 Ok(self
                     .get_rules_for(<$marker>::KEY)?
                     .0
@@ -121,8 +121,8 @@ impl DataProvider<PluralRangesV1Marker> for crate::DatagenProvider {
     }
 }
 
-impl IterableDataProvider<PluralRangesV1Marker> for crate::DatagenProvider {
-    fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+impl IterableDataProviderInternal<PluralRangesV1Marker> for crate::DatagenProvider {
+    fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
         Ok(self
             .get_plural_ranges()?
             .0
diff --git a/provider/datagen/src/transform/cldr/relativetime/mod.rs b/provider/datagen/src/transform/cldr/relativetime/mod.rs
index 4a90d45ba83..87805e62f0f 100644
--- a/provider/datagen/src/transform/cldr/relativetime/mod.rs
+++ b/provider/datagen/src/transform/cldr/relativetime/mod.rs
@@ -4,8 +4,8 @@
 
 use std::borrow::Borrow;
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use icu_relativetime::provider::*;
 use once_cell::sync::OnceCell;
@@ -94,8 +94,8 @@ macro_rules! make_data_provider {
                 }
             }
 
-            impl IterableDataProvider<$marker> for crate::DatagenProvider {
-                fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+            impl IterableDataProviderInternal<$marker> for crate::DatagenProvider {
+                fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
                     Ok(self
                         .cldr()?
                         .dates("gregorian")
diff --git a/provider/datagen/src/transform/cldr/time_zones/mod.rs b/provider/datagen/src/transform/cldr/time_zones/mod.rs
index 4a5bc7ea65e..0a4d96da379 100644
--- a/provider/datagen/src/transform/cldr/time_zones/mod.rs
+++ b/provider/datagen/src/transform/cldr/time_zones/mod.rs
@@ -2,6 +2,7 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use crate::provider::IterableDataProviderInternal;
 use crate::transform::cldr::cldr_serde;
 use cldr_serde::time_zones::bcp47_tzid::Bcp47TzidAliasData;
 use cldr_serde::time_zones::meta_zones::MetazoneAliasData;
@@ -9,7 +10,6 @@ use cldr_serde::time_zones::meta_zones::ZonePeriod;
 use cldr_serde::time_zones::time_zone_names::TimeZoneNames;
 use icu_datetime::provider::time_zones::*;
 use icu_datetime::provider::time_zones::{MetazoneId, TimeZoneBcp47Id};
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use icu_timezone::provider::*;
 use std::collections::BTreeMap;
@@ -69,8 +69,8 @@ macro_rules! impl_data_provider {
                 }
             }
 
-            impl IterableDataProvider<$marker> for crate::DatagenProvider {
-                fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+            impl IterableDataProviderInternal<$marker> for crate::DatagenProvider {
+                fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
                     if <$marker>::KEY == MetazonePeriodV1Marker::KEY {
                         // MetazonePeriodV1 does not require localized time zone data
                         Ok(vec![Default::default()])
diff --git a/provider/datagen/src/transform/cldr/transforms/mod.rs b/provider/datagen/src/transform/cldr/transforms/mod.rs
index 92fd6a8b52a..7392e92fde7 100644
--- a/provider/datagen/src/transform/cldr/transforms/mod.rs
+++ b/provider/datagen/src/transform/cldr/transforms/mod.rs
@@ -127,6 +127,7 @@ impl DataProvider<TransliteratorRulesV1Marker> for crate::DatagenProvider {
 }
 
 impl IterableDataProvider<TransliteratorRulesV1Marker> for crate::DatagenProvider {
+    // Don't do caching for this one. It uses its own mutex
     fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
         self.cldr()?
             .transforms()?
diff --git a/provider/datagen/src/transform/icuexport/collator/mod.rs b/provider/datagen/src/transform/icuexport/collator/mod.rs
index 48dd411d30c..72c5f6878a5 100644
--- a/provider/datagen/src/transform/icuexport/collator/mod.rs
+++ b/provider/datagen/src/transform/icuexport/collator/mod.rs
@@ -5,6 +5,7 @@
 //! This module contains provider implementations backed by TOML files
 //! exported from ICU.
 
+use crate::provider::IterableDataProviderInternal;
 use icu_collator::provider::*;
 use icu_collections::codepointtrie::CodePointTrie;
 use icu_locid::extensions::unicode::key;
@@ -12,7 +13,6 @@ use icu_locid::extensions::unicode::Value;
 use icu_locid::subtags::language;
 use icu_locid::LanguageIdentifier;
 use icu_locid::Locale;
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use std::convert::TryFrom;
 use std::str::FromStr;
@@ -137,8 +137,8 @@ macro_rules! collation_provider {
                 }
             }
 
-            impl IterableDataProvider<$marker> for crate::DatagenProvider {
-                fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+            impl IterableDataProviderInternal<$marker> for crate::DatagenProvider {
+                fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
                     Ok(self
                         .icuexport()?
                         .list(&format!(
diff --git a/provider/datagen/src/transform/icuexport/normalizer/mod.rs b/provider/datagen/src/transform/icuexport/normalizer/mod.rs
index 4d21087a859..3069ec34fdc 100644
--- a/provider/datagen/src/transform/icuexport/normalizer/mod.rs
+++ b/provider/datagen/src/transform/icuexport/normalizer/mod.rs
@@ -5,10 +5,10 @@
 //! This module contains provider implementations backed by TOML files
 //! exported from ICU.
 
+use crate::provider::IterableDataProviderInternal;
 use icu_collections::char16trie::Char16Trie;
 use icu_collections::codepointtrie::CodePointTrie;
 use icu_normalizer::provider::*;
-use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
 use std::convert::TryFrom;
 use zerovec::ZeroVec;
@@ -33,8 +33,8 @@ macro_rules! normalization_provider {
             }
         }
 
-        impl IterableDataProvider<$marker> for crate::DatagenProvider {
-            fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+        impl IterableDataProviderInternal<$marker> for crate::DatagenProvider {
+            fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
                 Ok(vec![DataLocale::default()])
             }
         }
diff --git a/provider/datagen/src/transform/mod.rs b/provider/datagen/src/transform/mod.rs
index 836684a5c0b..0ad46ed6529 100644
--- a/provider/datagen/src/transform/mod.rs
+++ b/provider/datagen/src/transform/mod.rs
@@ -31,7 +31,7 @@ impl DatagenProvider {
     {
         if <M as KeyedDataMarker>::KEY.metadata().singleton && !req.locale.is_empty() {
             Err(DataErrorKind::ExtraneousLocale)
-        } else if !self.supported_locales()?.contains(req.locale) {
+        } else if !self.supports_locale(req.locale)? {
             Err(DataErrorKind::MissingLocale)
         } else {
             Ok(())
diff --git a/provider/datagen/src/transform/segmenter/dictionary.rs b/provider/datagen/src/transform/segmenter/dictionary.rs
index bb77ac5339a..ead6b2120d9 100644
--- a/provider/datagen/src/transform/segmenter/dictionary.rs
+++ b/provider/datagen/src/transform/segmenter/dictionary.rs
@@ -2,6 +2,7 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use crate::provider::IterableDataProviderInternal;
 use icu_locid::langid;
 use icu_provider::datagen::IterableDataProvider;
 use icu_provider::prelude::*;
@@ -79,8 +80,8 @@ macro_rules! implement {
             }
         }
 
-        impl IterableDataProvider<$marker> for crate::DatagenProvider {
-            fn supported_locales(&self) -> Result<Vec<DataLocale>, DataError> {
+        impl IterableDataProviderInternal<$marker> for crate::DatagenProvider {
+            fn supported_locales_impl(&self) -> Result<Vec<DataLocale>, DataError> {
                 Ok($supported
                     .into_iter()
                     .filter_map(model_name_to_data_locale)