Country of origin, pretty much.
That used to meant deeper differences in mechanics, narrative and themes (that used to be about JRPG having more defined characters while WRPG having more customization; JRPG being mostly about anime fantasy while WRPG being about D&D fantasy; JRPG being turn based while WRPG being more action driven); but, in time, both genres informed the other to the point some games defy characterization (for example: Dark Souls being a JRPG that looks like a WRPG, Costume Quest being a WRPG that looks like a JRPG)
That used to meant deeper differences in mechanics, narrative and themes (that used to be about JRPG having more defined characters while WRPG having more customization; JRPG being mostly about anime fantasy while WRPG being about D&D fantasy; JRPG being turn based while WRPG being more action driven); but, in time, both genres informed the other to the point some games defy characterization (for example: Dark Souls being a JRPG that looks like a WRPG, Costume Quest being a WRPG that looks like a JRPG)