https://bugzilla.redhat.com/show_bug.cgi?id=1556854
--- Comment #7 from Mikhaylenko Alexander exalm7659@gmail.com --- ru_RU.UTF-8, but there's also Serbian, and e.g. Kazakh, Bashkir, Tatar etc. Also AFAIK Greek is also missing.
From wikipedia: Slavic languages: Belarusian, Bulgarian, Macedonian, Russian, Rusyn, Serbo-Croatian (for Standard Serbian, Bosnian, and Montenegrin), Ukrainian Non-Slavic languages: Abkhaz, Aleut (now mostly in church texts), Bashkir, Chuvash, Erzya, Kazakh (to be replaced by Latin script by 2025[18]), Kildin Sami, Komi, Kyrgyz, Mari, Moksha, Mongolian, Ossetic, Romani (some dialects), Sakha/Yakut, Tajik, Tatar, Tlingit (now only in church texts), Tuvan, Udmurt, Yuit (Siberian Yupik), and Yupik (in Alaska). https://en.wikipedia.org/wiki/Cyrillic_script