While we encourage people to use English on our server, we really don't want to force it's use by banning all others. No one can expect that someone would learn English in order to play (although playing can be an opportunity to learn), and placing such a barrier is just too much for a game that is supposedly open for everyone.
As for the question why only the Cyrillic charset is supported (besides the Latin one), the answer is simple: the game originated in the Cyrillic-using world, for the most part it was exclusively developed by the Cyrillic users, and was played by them. Cvet himself, the engine developer, is a Belorussian. Cyrillic support was natural. Disabling it in chat would change nothing - except, perhaps, some Russian/Belorussian/etc. players would feel muted, while others will simply use translit, and will be equally incomprehensible.
Disabling the Cyrillic nicknames is, however, another thing. There are few features, with prospects for more, that require players to write other players' nicknames. Simple lack of knowledge about the Cyrillic keyboard layout can be an obstacle. This will be given more thought in future, but I can't say at this moment when, and what the outcome will be. And this is an honest "no idea" spoken here.
