Language fallback

I think that many editors who contribute in Belarusian are programmers. They usually have intermediate knowledge of English. On the other hand if a person doesn't know English, he can easily switch to Russian interface.

Good point: while editors might be programmers, thousands of Wikipedia users (visitors) are probably not. Moreover, Belarusian speakers who don't know English may currently be forced to switch to Russian, while they would prefer to use the Belarusian interface where possible.

So, if you're right, we should add the fallback to make more people use the Belarusian interface, and not worry about the editors who can always change their preferences (unlike unregistered users).