Mimetex currently supports the following font families: cmr10, cmmi10, cmmib10, cmsy10, cmex10, bbold10, rsfs10, stmary10 and wncyr10 with symbol "names", e.g., \alpha \beta \forall \sqcup, etc, identical to your usual LaTeX expectations. Russian/cyrillic is wncyr10, and is invoked in mimetex by writing {\cyr ...}. For example, $$$\sqrt{\frac{\cyr Khrushchev}{2}}$$$ renders 
(though the mathematical significance of that particular expression escapes me). And note that mimetex also recognizes the usual cyrillic ligatures.
But you wrote me a separate, more detailed, email that complicates your above question. It's reproduced below, hopefully with your permission, since it contains nothing that seems private to me:
Hello,
As far as I know Moodle use mimetex for mathematics formulas. Moodle use utf-8 encoding. Moodle have LaTeX preamble, which I can change...
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\RequirePackage{amsmath,amssymb,latexsym}
Can I tune mimetex for using non-ASCII (for example, Russian) symbols in formulas? I try this Latex preamble, but it doesn't help:
usepackage[T2A]{fontenc}
usepackage[utf-8]{inputenc}
usepackage[russian]{babel}
usepackage{amsmath}
usepackage{amsfonts}
RequirePackage{amsmath,amssymb,latexsym}
Best regards,
Artem Andreev
Mimetex doesn't use any LaTeX preamble at all. So your preamble change won't help, as your email noted.
But moodle's math filter also uses a standard teTeX distribution of (La)TeX if your server has one installed. In that case, you're not using mimetex at all. And I suppose your preamble change should have some effect. But you'll have to ask the person who wrote this moodle filter why it didn't work the way you expected.
If you don't have teTeX installed, then you're probably using mimetex, and changing the math filter's preamble won't affect anything at all. But you don't need to change the preamble. The {\cyr ...} syntax illustrated above should work for you if you want cyrillic characters.
Note: The version of mimetex distributed from moodle's site is rather old, and doesn't contain any cyrillic support. Go to http://www.forkosh.com/mimetex.html amd download mimetex from there. That's always the current version, and supports cyrillic as illustrated above.
But you wrote me a separate, more detailed, email that complicates your above question. It's reproduced below, hopefully with your permission, since it contains nothing that seems private to me:
Hello,
As far as I know Moodle use mimetex for mathematics formulas. Moodle use utf-8 encoding. Moodle have LaTeX preamble, which I can change...
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\RequirePackage{amsmath,amssymb,latexsym}
Can I tune mimetex for using non-ASCII (for example, Russian) symbols in formulas? I try this Latex preamble, but it doesn't help:
usepackage[T2A]{fontenc}
usepackage[utf-8]{inputenc}
usepackage[russian]{babel}
usepackage{amsmath}
usepackage{amsfonts}
RequirePackage{amsmath,amssymb,latexsym}
Best regards,
Artem Andreev
Mimetex doesn't use any LaTeX preamble at all. So your preamble change won't help, as your email noted.
But moodle's math filter also uses a standard teTeX distribution of (La)TeX if your server has one installed. In that case, you're not using mimetex at all. And I suppose your preamble change should have some effect. But you'll have to ask the person who wrote this moodle filter why it didn't work the way you expected.
If you don't have teTeX installed, then you're probably using mimetex, and changing the math filter's preamble won't affect anything at all. But you don't need to change the preamble. The {\cyr ...} syntax illustrated above should work for you if you want cyrillic characters.
Note: The version of mimetex distributed from moodle's site is rather old, and doesn't contain any cyrillic support. Go to http://www.forkosh.com/mimetex.html amd download mimetex from there. That's always the current version, and supports cyrillic as illustrated above.
Thank you very much! I try and it work! Thanks!