How long do you find it takes for you to lose some ability in the languages you know? if at all? I'm finding this lately, in little bits here and there across my entire list of languages. Hesitancy when speaking in French, briefly forgetting an important German verb when writing something, an inability to understand old notes in Sumerian or Akkadian when I try to pick them up again and so on.
It is deeply irritating.
Will not answer questions which only need a basic knowledge of grammar. Pay attention to the textbook.