OK, I haven't activated 'Translatable' for widgets...
Object::add_extension('Widget', 'Translatable');
Object::add_extension('WidgetArea', 'Translatable');
But there is also a bug because when adding a widget now, it will be created for 'en_US' instead of the current language
Here is my config:
Translatable::enable();
Translatable::set_default_lang('de_DE');
Translatable::set_default_locale('de_DE');
// Set the site locale
i18n::enable();
//i18n::set_locale('de_DE');
i18n::set_default_lang('de_DE');
i18n::get_tinymce_lang('de_DE');
I have german (de_DE) and english (en_GB!) pages and there are no problems by switching the language, only the widget areas doesn't work probably. Pages will be save in their language and widgets as Locale = 'en_US'?! Because of that I can't see the added widgets in the backend.