A translation of the English sentence "Nobody sang except me" into Spanish would be "Nadie cantó excepto yo". Why does the object pronoun in English become the subject pronoun in Spanish?
You certainly gave me food for thought. Maybe this trick will suffice to explain: rephrase to get the 'subjects' together:
Nadie excepto yo cantó.
Music to my ears. I would say that Spanish is 'functionally consistent' in this case. Is the trick valid in English?
Nobody except I sang.
I think that sounds correct, but I'm not a native speaker so won't conclude on it. However when using but instead of except it really comes out: nobody sang but I / Nobody but I sang'... Which looks kind of weird but I would think those are the right way to use them, the same way one should answer 'it is I' to the question of 'who is it?'
PS 1: in grammatical terms, the use of 'yo' (subject pronoun) vs 'mi' (object pronoun) makes perfect sense because I is the person who carried out the act of singing (actually, the only one because no one else joined, right? ;)) So it is actually English the one that is kind of breaking it because Spanish (as I said before) is doing it consistently.