I don't understand the problem.. Why is it possible for others to do a multi lang version of this miui version and you can't? I will not give any rom build names, only if I am allowed, but they are on Xda.
Many XDA roms have multi language roms from miuiandroid. They don't develop it by themselves.
But most errors here are from new translators who yet don't fully know about how to properly translate xml.
The roms are you talking about have less languages. We have more new langs and actively deal with error.
So please wait for bug fixes and when it's done then it's done. And if you have time and knowledge provide logcats from errors that you encountered.