If you have an application in the iTunes App Store then you might be considering localizing it to improve sales outside the US. In addition to translating the application’s user interface, you’ll need to translate the App Store description and keywords. There’s a gotcha when you try to submit keywords for the multibyte languages (Chinese and Japanese).
According to Apple’s documentation (pdf), Keywords can be single words or phrases and the text field is limited to 100 characters. In fact they mean to say 100 bytes. This is a minor point, but when you translate your keywords into Chinese or Japanese, they will more than likely exceed 100 bytes. I had to trim mine down, for example, to 41 characters in Simplified Chinese, to fit into the 100 byte limit.

I haven’t attempted to exceed this, but the 255 character limit on your application’s name is possibly also 255 bytes. Likewise, the application description is probably 4000 bytes instead of the documented 4000 characters.

Keep it mind when planning your localization, especially if you are getting estimates for the translation of your application’s descriptions and keywords. Hopefully you won’t have to pay for something that you can’t even use.

Update: Kirby’s comments remind me that this problem is only apparent after you update the application. If you merely add the description and keywords when appending a new language translation, you won’t see the problem. That is to say, you’ll think the keywords were accepted, but they are probably truncated if more than 100 bytes.