[MM-60792] Add support for loading experimental (e.g., in progress) languages (#29009)

* Add support for loading experimental (e.g., in progress) languages

* Fix e2e config

* Improve language labels

* Improvements

e2e-tests/playwright/support/server/default_config.ts

@@ -509,6 +509,7 @@ const defaultServerConfig: AdminConfig = {
         DefaultServerLocale: 'en',
         DefaultClientLocale: 'en',
         AvailableLocales: '',
+        EnableExperimentalLocales: false,
     },
     SamlSettings: {
         Enable: false,