language consistency in anime credits
My opinion is that from what country the studio originates from has that language, and let us say a Japinese movie is going to be dubbed. Well, they aren't going to redo everything or it wouldn't be the same... So they change the voices and the ending maybe because of the intro. If it stays in the Japanese language, maybe it shows where it originates and they add the subtitles so some viewers know what the song is saying.