I just rembered, and I have to tell you :)
I'm speaking a lot of (written) English, and here's an example of what happenes when in your head you live in both languages (and before you ask: yes, I sometimes dream in English, and when I'm really angry I think in English as well):
For a reason I cannot remember, I had been writing my former colleagues an e-mail and in that asked them to wish us luck (I think we tried for a lottery win)
What I wanted to say was the German expression "Haltet die Daumen gedrückt" (Keep your thumbs squeezed)
And what did I say? "Haltet die Finger gekreuzt." and that translates directly to "Keep your fingers crossed."
Instead of using the German phrase I just translated the English one. And only noticed it when one colleage wrote back "In German we say Haltet die Daumen gedrückt. But we understand you :) "
I could laugh about this every time I think about it *gg*