feat: Support multiple languages at once in builds (#2994)

* aria-supported doesn't throw if multiple languages used

* include info on targeting multiple languages in readme

Gruntfile.js

@@ -110,6 +110,9 @@ module.exports = function(grunt) {
       data: {
         entry: 'lib/commons/aria/index.js',
         destFile: 'doc/aria-supported.md',
+        options: {
+          langs: langs
+        },
         listType: 'unsupported' // Possible values for listType: 'supported', 'unsupported', 'all'
       }
     },

README.md

@@ -101,7 +101,7 @@ or equivalently:
 
 `npm run build -- --lang=nl`
 
-This will create a new build for axe, called `axe.<lang>.js` and `axe.<lang>.min.js`. If you want to build localized versions, simply pass in `--all-lang` instead.
+This will create a new build for axe, called `axe.<lang>.js` and `axe.<lang>.min.js`. If you want to build localized versions, simply pass in `--all-lang` instead. If you want to build multiple localized versions (but not all of them), you can pass in a comma-separated list of langages to the `--lang` flag, like `--lang=nl,ja`.
 
 To create a new translation for axe, start by running `grunt translate --lang=<langcode>`. This will create a json file fin the `./locales` directory, with the default English text in it for you to translate. We welcome any localization for axe-core. For details on how to contribute, see the Contributing section below. For details on the message syntax, see [Check Message Template](/docs/check-message-template.md).
 

build/tasks/aria-supported.js

@@ -16,9 +16,8 @@ module.exports = function(grunt) {
        * as `axe` does not exist until grunt task `build:uglify` is complete,
        * hence cannot be required at the top of the file.
        */
-      const langOption = grunt.option('lang');
-      const fileNameSuffix =
-        langOption && langOption.length > 0 ? `.${langOption}` : '';
+      const { langs } = this.options();
+      const fileNameSuffix = langs && langs.length > 0 ? `${langs[0]}` : '';
       const axe = require(`../../axe${fileNameSuffix}`);
       const listType = this.data.listType.toLowerCase();
       const headings = {