Are the supported languages in-game or from the installers or perhaps both? It seems unclear to some.

Setup.ini contains the key values of supported languages

http://redump.org/disc/25117/

PX-760A (+30), PX-W4824TA (+98), GSA-H42L (+667), GDR-8164B (+102), SH-D162D (+6), SOHD-167T (+12)