Cloud edition language?

Can each user in cloud edition have his own language for their interface ? if not, can it be implemented

No. This is a global preference. Read the Guide: Manager Cloud

Yes, I understand but imagine if I’m an accounting Firm?? My clients could want their own languages. Think about it. It would be very good to have it.

This was actually tried for a short while, with the ability to set language by business. But there were problems with implementation and the concept was abandoned.

It would be good to have it