[mitchty]

Yes, encoding and character sets are difficult. Having say even a simple ü in your password brings up a ton of encoding nightmare. Solvable nightmare, but not one i'd want to tackle for passwords. Could they be used, sure, but there is a lot to it. Also you can turn off the simple lock numeric lock screen and use the japanese keyboard if you want (or any others you've turned on). Just swipe off simple passcode under passcode lock.

[evoxed]

I've never used the simple lock– I have a long passphrase that I prefer. It still won't let me change keyboards, despite setting the OS language being set to Japanese. It's up-to-date software wise, but was purchased in the US so...