Only include langs with enough translation in the in-app language switch

When a language has too many crucial strings missing, it should not be shown in the app language switcher. Examples are 'Connect' or 'Unsecured Connection'.

These half-translated languages (I'd call them broken) would still be shown to users who have that have their system language set to this specific language (or it can be picked up through the Android l10n fallback system).

@cyberta preferred to not remove the existing translations that cover only a part of the app with the argument of not breaking an existing situation for an existing user base.