Fields that are not localized should not be editable in the language that is not the primary one

[rolfsdMediaMarktSaturn]

When a field does not have localisation activated, its value can currently still be edited in the other language. If the content editor is not aware, he then mistakenly changes/ overwrites the language of the field, even though that's not what he wants. Please make it so that i can choose a primary language and all fields without localisation activated should not be editable in the secondary languages.