We thought about that quite a lot at @w3c_wai last year, and the best solution we could come up with was listing all languages in the header and in the sidebar (one location probably would be enough), in the target language + the standard translations icon w3.org/WAI/fundamentals/acce…

“česky, čeština” (adverb and noun) doesn’t make sense (to me). Use either, but not both. `text-transform: capitalize` doesn’t work well for “русский язык”; the я shouldn’t be capitalized, I think. Quick fix: omit “язык” (“language”), “русский” alone will do.