Just recently our company started developing WEB version of our product and our testers keep writing tests to verify that UI controls can correctly display unicode characters. Does it make much sense to do that if all our control if they are all HTML/JavaScript based?
You should ideally channel all character/encoding handling through one channel which can be tested and validated once. If there's a chance that every single page and widget may behave differently with regards to encodings, you have a bigger problem. You want to nail encodings once, then concentrate on other problems.
Having said that, more tests are hardly ever bad. Only if you start obsessing about and testing the same thing over and over I'd start to worry about some root causes.
See also: Joel Spolsky's "The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!)" http://www.joelonsoftware.com/articles/Unicode.html