As in in pictochat and user names? If so no I don't think it is available, unless it is part of Japanese having Greek letters and the like which a quick scan says not so much. Even if you did hack it in then the games which pull from it would probably only show garbage unless you hack those as well.
If you mean in games then if you hack in the characters to the font (or again it comes as part of Japanese set -- http://www.rikai.com/library/kanjitables/kanji_codes.sjis.shtml is not always complete in games but it usually has a lot and it is not like Cyrillic is a large alphabet) there is no reason why not. Other than the Japanese stuff then you are going to have to play hacker for anything good.
Russian speaking game hackers and translators are a good bunch as well, not sure what the current sites are for Russian stuff but start with gbx.ru and go from there.
There are a handful of Russian DS games, mostl kid stuff and film tie ins.
6069 Madagascar 3 - Europe's Most Wanted Europe Eeprom - 4 kbit 512 Mbit
5254 Hardy Boys - Treasure on the Tracks, The Europe Eeprom - 512 kbit 1024 Mbit
4120 Successfully Learning Mathematics Europe Eeprom - 4 kbit 512 Mbit
3824 Disney Fairies - Tinker Bell Russia Eeprom - 64 kbit 512 Mbit
3645 Love is... ...in Bloom - The Flower Shop Garden Europe Eeprom - 4 kbit 128 Mbit
3645 Love is... ...in Bloom - The Flower Shop Garden Europe Eeprom - 4 kbit 128 Mbit
3392 Travel Coach - Europe 3 Europe Eeprom - 64 kbit 1024 Mbit
3392 Travel Coach - Europe 3 Europe Eeprom - 64 kbit 1024 Mbit
3109 Ankh - Curse of the Scarab King Europe Eeprom - 64 kbit 1024 Mbit
1367 Pirates of the Caribbean - At World's End Russia Eeprom - 4 kbit 512 Mbit
List generated from http://www.advanscene.com/
I saw the PSP has quite a few games in Russian, including some not kid ones.
If you want a hand with hacking things then my Russian is not so good these days but I remember enough of the grammar and setup that I can help there if you want, and more general hacking concepts I am fine with.
Ah OK you are making homebrew.
In that case I imagine the devkitpro devs will do anything with extended ASCII (too many different standards and it is a nightmare to keep them all in line) and it is probably all going to be unicode instead.
Afraid I have not tangled with this here, however you might like CLIRC https://code.google.com/archive/p/clircds/source/default/source which is an IRC client written by a Russian dev aiming at handling Russian characters as part of it all.
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