Not sure the german market for point & click is still as big as it was.
I usually play the games in English if the game was created in English. Or when there is English voice over and German texts I switch to English subtitels, because I find it very distracting when you read something else than you are hearing.
Most Germans understand English well enough. But for some it feels more like "work" playing in a different language, which contradicts the "having fun" part of playing a game. So they don't play if there is no translation. (I guess it's the same in France, Italy, Spain...)
Google translation would be better than none, I guess, but only for a free game. But make sure you tell the player in advance that it is a google translation. These translations are sometimes hard to understand. For a commercial game I would not risk it. That is a shitstorm waiting to happen.
No idea about the costs. A quick search came up with about 0,15- 0,20 € per word or 0,80 - 2,50 € per line. There is quite a range here.