I've seen other reports about other non-english characters not working as well. I'm not sure if the issue is because the fonts which are included with Photoshop Touch don't include these characters (even though they appear with the native keyboard layout). Regardless, I'll pass the info on to the Photoshop Touch development group to ensure they are aware. Thanks for posting about the issue.
Anyone who wants to let the product team know how much they would like to have Chinese, Japanese, and Korean alphabets supported in Photoshop Touch, should vote for the feature suggestion in our Ideas section.