ARMA2 key and language version

[cowkof 10]

I've got the following question.

I tried to install ARMA2 from a (downloaded) english version ISO file.

All worked well, I used my key which I got from my original buying.

After starting the game, it was in english.

But .... after updating the game it went back to german.

So here is my question:

Is there any language 'definition' in my key or am I doing something wrong ?

Thanks for an answer.

PS

If I do something wrong, can someone explain me how I can get the english game running without using the language packs.