Does a MIUI-Phone work in Europe? I've just read about the chinese MIUI Phones (Mi Two), my question is wheter they work in Europe, or might there be some issues because of other phone networks? Might there be some other issues apart from that? 

Bonus Question: Does the official MIUI-Rom has any other languages than Chinese?
According to GSMArena, the Xiaomi Mi-Two supports the following frequencies:

2G Network: GSM 850 / 900 / 1800 / 1900

3G Network: HSDPA 850 / 1900 / 2100

You can check what frequencies your country uses here. It should work in most if not all EU countries though. 

Also, it supports Chinese and English officially but there is unofficial support for other languages, located here.