Re changing route: I don't think you can do it interactively. The best bet is to start driving and hope for rerouting. As far as I remember, modRana has rerouting logic implemented, but I am not sure whether its exposed in the current code.

Re espeak-English vs German: no wonder . There are better TTS engines available, some with German support. But they would have to be interfaced from modRana as well as selection of language for routing instructions.