can I give away Titan Quest (german)

I think yes. If you not sure i would take it from you :)

not on public but you can create a private one

U can give key to me :D

it should be okay if you create a private giveaway or give it away in a german group.

a better approach to get a 100% answer is to create a support ticket (yeah, I know, so little mods, so many tickets)

Btw: it's possible to change the sounds and texts from German to English, I've done so myself (use google).

I gave one away a while ago.
I would say something similar should be fine.

Store page is HERE.

I received one ago, and when activated on steam, it just said that german language only available in Germany, and it came up to be english version.