No, not thinking of singing. There could be more, but there is definitely at least one more main character who has played an instrument, and one where the person playing the instrument was not a main character, but became one in the next series.
Oh yeah: Scotty played the bagpipes at Spock's funeral. Ironic since James Doohan IRL was missing a couple of fingers due to a war injury -- it was physically impossible for the actor to play that instrument. Otherwise: Keiko O'Brien played clarinet on TNG, before the two O'Briens crossed over to DS9. I don't recall Miles ever playing anything, however (and I wouldn't consider Keiko to be a "main" character, only a recurring one.) On the language question: I still haven't figured out the language spoken by the Yellow Pages folks in TVH. I did find out that the crew of the whaling ship in the same movie spoke Finnish.
That's the one. The other main character I was thinking of was Jadzia playing the keyboard in Equilibrium. I forgot about Scotty.
Harpsichord, I think. Janeway plays some unnamed musical instrument in the episode "Remember." I don't know if this counts, as this is not a real instrument.
Who was that girl who played the violin (I think) and later the roll out piano with Picard? I think they dated that episode too.
I'll see your answer and raise it- English, French, German, Russian, Spanish, Swahili and for the win, L-A-T-I-N
I'm not gonna call my post a win (pride goeth before destruction ) but I can add one more. Da Vinci speaks Italian in VOY. And I know the original question says "how many real languages do we hear spoken on Trek?" but I'm still going to mention TNG's Loud as a Whisper, which contains quite a few examples of American sign language.