[4.2] install language - an error message when no xml is returned

[jgerman-bot]

New language relevant PR in upstream repo: joomla/joomla-cms#38113 Here are the upstream changes:

Click to expand the diff!

diff --git a/administrator/components/com_installer/src/Model/LanguagesModel.php b/administrator/components/com_installer/src/Model/LanguagesModel.php
index d97dccc0a319..12bdde329517 100644
--- a/administrator/components/com_installer/src/Model/LanguagesModel.php
+++ b/administrator/components/com_installer/src/Model/LanguagesModel.php
@@ -152,6 +152,14 @@ protected function getLanguages()
 		}
 
 		$updateSiteXML = simplexml_load_string($response->body);
+
+		if (!$updateSiteXML)
+		{
+			Factory::getApplication()->enqueueMessage(Text::sprintf('COM_INSTALLER_MSG_ERROR_CANT_RETRIEVE_XML', $updateSite), 'error');
+
+			return;
+		}
+
 		$languages     = array();
 		$search        = strtolower($this->getState('filter.search'));
 
diff --git a/administrator/language/en-GB/com_installer.ini b/administrator/language/en-GB/com_installer.ini
index 90c1d9895ab4..245f636c802d 100644
--- a/administrator/language/en-GB/com_installer.ini
+++ b/administrator/language/en-GB/com_installer.ini
@@ -144,6 +144,7 @@ COM_INSTALLER_MSG_DISCOVER_NOEXTENSION="<strong>No extensions have been discover
 COM_INSTALLER_MSG_DISCOVER_NOEXTENSIONSELECTED="No extension selected."
 COM_INSTALLER_MSG_DISCOVER_PURGEDDISCOVEREDEXTENSIONS="Cleared discovered extensions."
 COM_INSTALLER_MSG_ERROR_CANT_CONNECT_TO_UPDATESERVER="Can't connect to %s"
+COM_INSTALLER_MSG_ERROR_CANT_RETRIEVE_XML="Can't retrieve XML from %s"
 COM_INSTALLER_MSG_INSTALL_ENTER_A_URL="Please enter a URL"
 COM_INSTALLER_MSG_INSTALL_INVALID_URL="Invalid URL"
 COM_INSTALLER_MSG_INSTALL_INVALID_URL_SCHEME="Please enter a valid URL starting with http or https."