Don't quote me but I thought the language switching on PS4 is hardcoded to ~ on PS4 (if you have multiple language inputs set up). Which incidentally, many others on PS4 had difficulty trying to bind ~ key to an action as it is tightly bound to PS4 OS-level.

On quick search, someone posted a problem on the forum a month or so ago: http://forum.square-enix.com/ffxiv/t...Japanese-input