Technical term for the loss of words in your mother-tongue when speaking a different language I am basically looking for two words which are, though, related to some degree. It might even be that ultimately the same word is the answer to both parts of this question.
I split them up into two questions. That's the related question.

Anyhow, here's what I'm trying to give it a name.
My mother-tongue is German. I, obviously, speak German very fluently and can convey any kind of ideas. However, if I speak in English for a while and then have to translate something into German, I sometimes fail to come up with German phrases. In that very moment, only English idioms come to my mind. Under different circumstances I certainly could say it in German, but right in that moment I feel like German would be my second language.

Is there a technical term for the inability to express certain things with words or phrases which you actually know by heart and that you would use off-the-cuff under normal circumstances?
It seems to me that it'd be a type of a tip-of-the-tongue phenomenon caused by bilingualism. If you don't use German regularly, it might be attributed to language attrition, but this seems unlikely if you're still being exposed to German more than English.

http://en.wikipedia.org/wiki/Tip-of-the-tongue_phenomenon#Effects_of_bilingualism