I understand you can create links where UTF8 figures are encoded, but can you really really match individuals figures within rewrite rules? Example being just rewrite a static page in utf8 cyrillic russian text with a other page.

Yes it’s possible:

RewriteRule ^de/b\xC3\xA4ume$ en/trees [L]

This can match /de/bäume and rewrite it to /en/trees.