I haven't got one of those cameras to test it with but it works irrespective of the language setting on the GX80/85 so I can't see why it wouldn't from the point of the commands.
However, I would say you should test it yourself before buying it just in case there is something different in the firmware of the Japanese version (and there might possibly well be) that stops it from working.
nielsviv got a reaction from BTM_Pix in Would You Perhaps Be Interested In A Different GX80/85 Colour Profile???