fix(lang) fix default language selection

[0] introduced sorted language keys, but we had the assumption that the
first one meant to indicate the default language.

Break that assumption and be explicit about English being the default
language.

[0]: 7fe319d965

react/features/base/i18n/i18next.js

 /**
  * The available/supported languages.
  *
- * XXX The element at index zero is the default language.
- *
  * @public
  * @type {Array<string>}
  */
 /**
  * The default language.
  *
- * XXX The element at index zero of {@link LANGUAGES} is the default language.
+ * English is the default language.
  *
  * @public
  * @type {string} The default language.
  */
-export const DEFAULT_LANGUAGE = LANGUAGES[0];
+export const DEFAULT_LANGUAGE = 'en';
 
 /**
  * The options to initialize i18next with.