According to their page it's a pure searxng instance. I didn't see anything on my own instance changing so there are three options I see:

• The mentioned server side changes (e.g. A server move you mentioned but could also be server settings, provider settings, etc).
• client side changes: somehow your Firefox provides different information to alter the results
• subjective change: it's always a possibility that either what you searched or your perception was more fine tuned to Cyrillic.

And then there's the obligatory "none or all of the above".

Personally I'd guess it's just a fluke. I gave it a few searches from Firefox mobile on "all languages" and had a mix of mainly English and a bit of German und French in there as results.

Edit: if you're comfortable with that feel free to share some search terms and we can compare results. Would be curious myself!

Huh, and for me Searx hasn't been great for searching in Russian in particular.

I experienced the same problem and the workaround was to select English from the Default Language dropdown menu (after performing a search). I switched to another instance anyway.