The following characters are not supported by Minecraft:
Ҙ ҙ Ҡ ҡ Ҫ ҫ
These characters are used in Bashkir, but are not supported by Minecraft, as opposed to other Cyrillic characters.
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The following Bashkir letters are not supported: Ҙ ҙ Ҡ ҡ Ҫ ҫ

On a related note, the Tajik letter Ҳҳ appears to be missing in default 1.14.4
@unknown, please create a new ticket for that, if we don't have one already.
Edit: Tajik is not supported by Minecraft as of now, so I'm not too sure whether that ticket would be valid.
Upon checking the creative menu there appears to also be an E-like character (not the one in relates to) which is also missing