MDL-68271 core_h5p: implement localization methods for editor
The following methods have been implemented for supporting
content-type translations:
- H5PEditorAjaxInterface.getTranslations. This method is used for
loading the "Text overrides and translations" section.
- H5peditorStorage.getLanguage. This method is used for displaying
the specific fields and messages for each content-type library.
- H5peditorStorage.getAvailableLanguages. This method is used to
get the language list displayed into the "Text overrides and
translations" section.