Whatever you're putting in your .def must be the same route as the folder, in the example you provided I guess you put:
stages/太陽の畑/Flower Land.def
However once you extract the file you get this route:
stages/Garden of the Sun/太陽の畑 Which is what you have to put in your select.def (plus the file name of the stage of course).
But you can get rid of all the extra folders and just put the files inside stages, so you'll get:
stages/Flower Land.def
It'll work that way too. If the music doesn't change the route inside the stage file (Flower Land.def).
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