Does anyone know if spotify downloads duplicate songs?
Like if I have two of the same song in different playlists and I download both playlist, is it going to download both songs?
Short answer: No.
Long answer: spotify will not download a song again if it has the same id. Just make sure that you put the same version of the song in both playlists (like both are from the same album, have the same title, isn't a remaster, etc)!