I was thinking of the scene where the Klingons engage V'ger while their battle music is playing. Is that also playing in-universe by a Klingon orchestra on one of those ships (similar to how music was played for Immortan Joe's forces in Mad Max: Fury Road)? Or maybe Klingon Captain Mark Lenard is playing it off an mp3? Semi-serious, but do you think other theme music exists in Trek? Maybe the TMP/TNG theme is the Federation National Anthem?
I always wanted it to be, but alas, no. We heard the Federation Anthem in DS9: "Take Me Out to the Holosuite," and it was composed for the episode by David Bell. I thought this thread was going to be more about diegetic music in the movies, like "The Moon's a Window to Heaven" or "I Hate You."
If someone ever does the "edgy" dystopian Star Trek where the Federation is in shambles and stuff I Hate You should be established as Earth's new national anthem.
There are always playing "The Little Warrior and his Targ" in the background, just most humans don't know that its a Klingon song, since no one sings the lyrics anymore.