I created a Japanese iTunes account, and legitimately purchased some tracks I was keen on listening to. Easy! Getting Spotify to play nice however, has been anything but.

So I added my tracks to a playlist, and set it to download. I hook my Nexus 6P up to the same Wifi, and the songs download.

That is, the songs in the Spotify library. The local tracks do not download. At first, I thought it was because the files were AAC encoded. No problem! I converted them to MP3 (and moved them to a seperate folder, so I wasn't getting mixed up). No dice - they don't all go across.

My next thought was perhaps the Japanese characters in the tags, or perhaps the file names. No problem - I can remove those and convert them to english equivalents! However, after re-importing them (by removing all local files then letting spotify find them again), the files will not sync to my 6P reliably.

A few other tidbits that may be interesting to note:

1. I have 81 setlist tracks totalling 9.4GB. They sync across to my 6P just fine.
2. I've correctly added the tracks to a list, and the Japanese ones don't sync reliably.
3. Some of the tracks show up in mobile, but they're all greyed out.
4. I have added 15 Japanese tracks to my list, but only 6 show up (and as mentioned in the previous point, they're greyed out).

Some other stuff I've tried (to make sure we get the easy stuff out of the way)

1. Yes, the list is set to "Downloaded" on desktop and Mobile.
2. A seperate playlist of more tracks and larger files downloads correctly to mobile.
3. I created a seperate list with just those tracks and added my local files. Of the 15 tracks I added, only 4 are listed in this new list, and no files have synced (the tracks that are in the list are greyed out)
4. I've reinstalled Spotify on Windows and on my Nexus 6P.
5. I removed all my offline devices from https://www.spotify.com/account/offline-devices/, and tried again - no dice.

Thanks in advance for any help! Let me know if I've missed anything or if anyone has a suggestion.