Creuza de Mä
Thanks to Mike and his vacation video, I have gone through half the day with Journey's "Don't Stop Believing" stuck in my head.
Fortunately, eMusic came through with some Jordi Savall follie and a version of Fabrizio de Andre's "Creuza de Ma", sung as a duet by Mauro Pagani (who co-wrote it with de Andre) and a Catalan singer named Joan Isaac. The song is on Isaac's album, but appears to have been recorded at one of Pagani's concerts. The two singers sing alternate verses; Pagani in the original Genovese, Isaac in Catalan.
In terms of musical and linguistic obscurity, it may represent some kind of local maximum.
Umbre de muri muri de mainé dunde ne vegnì duve l'è ch'ané da 'n scitu duve a l'ûna a se mustra nûa e a neutte a n'à puntou u cutellu ä gua.