Just want to mention that the PSP game I'm working on happens to use UTF-16LE, so it might be worth checking for that encoding too. (Along with the usual ones like Shift-JIS, UTF-8, etc). GBAtemp seems to have a slightly active PSP Hacking & Homebrew section, so you could search for topics on that site / try asking questions there if people here don't have answers.
That said, I mostly stick to translation and testing at the moment, so I probably can't help much beyond that.