The same problem is by me, opera shows squares instead of Armenian letters, the fonts in other languages have been also changed. This happened after opera's self-update to 25, I have changed encoding and fonts but nothing helped, any ideas else?
Open opera://flags/#disable-direct-write (paste this link to address bar) and in the "Disable DirectWrite" section press Enable button.
Mersi!! Rammstein für immer 🙂 finally Opera shows Armenian letters!