As far as I know we can not change the url label through the language files. So the only way to change questions to topics is by using the constant_path_map method.
So, we can do it, but if we do it we have no way to define topics as homepage.
This is the problem.
It is necessary because on sub categories the script jumps again into questions/... urls, as the setting we can do is only for the homepage.
So i need both, redirect questions as homepage AND topics instead of questions on sub categories.
Actually I see that we can have only one thing, tranlated url parts or the freedom to define a homepage.