Just wasting your time. Some features don’t work as described.

Any particular problems? Everything should work as described, but since there are thousands of other plugins and themes, sometimes there are conflicts. I do respond to all support requests and am interested in ironing out compatibility problems, in case such problems occur.

I tried adding highlights for Cyrillic text, and it works on my test site: https://prnt.sc/v1i0b6

Your settings seem fine to me. What’s the search term on that search results page?

The excerpts seem to match the settings, so everything should be fine on the theme end – but to make sure, is the theme using the_excerpt() to print out the excerpts, without any other modifications?

If you do the same search with the Relevanssi admin search (Dashboard > Admin search), does the highlight work there or not?

So no highlights even in the Relevanssi admin search (I’m not talking about general admin search, but specifically the Relevanssi admin search under Dashboard > Admin search)? That rules out issues with the theme, your theme is likely fine then.

Have you tried disabling other plugins and have you tried doing a search while live previewing one of the WP default themes? It’s possible Relevanssi is creating the highlighted excerpts just fine, but something else is stripping the tags that add the highlights. That can happen, and Relevanssi can do nothing about that.