Karen Johnson has a nice post here about the most basic tests she does when confronted with an application that should handle multiple languages:
So when it was time to choose a handful of languages to test with, my reaction was to choose:
1. one or more Latin-based languages
2. one or more languages with a heavy use of diacriticals
3. a RTL [Right-to-left] language
4. a language that is more symbolic than character-based
A common problem in testing with these languages is the lack of keyboard or a means of entering characters from different languages. Cut and paste can work if you’re careful.
You know, that’s a handy set of tests for anytext-accepting control on any Web site, even if your application only expects and only accepts (allegedly) English.