Vim doesn't work properly with cyrillic symbols

I'm trying to learn vim by its built-in tutorial. It is in russian so all the symbols are cyrillic. The most interesting thing is that vim commands doesn't seem to work with them. For example, I'm trying dw in normal mode with russign symbols, it deletes sometimes 1, sometimes 2 symbols within the word. It doesn't delete the whole word. But it works fine with latin letters. What's the reason?