[Users] How can I install alternate dictionaries?

[Removed GDPR]

Thanks for this info. I actually saw in YaST that I already had
myspell-en_US installed so I installed also myspell-bg_BG. Then in
preferences I could select the later one as alternate dictionary and
enable spell checking with both. However when typing a message -
anything typed in Bulgarian gets highlighted as wrongly spelled, i.e.
spell checking works only for English.

Any idea how to make it work properly?