Joel Spolsky's 'The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!)' is a good start: http://www.joelonsoftware.com/articles/Unicode.html

Like a few other specialised fields (cryptography comes to mind) the key takeaway is to use a library and rely on the work of people who know it better than you do and have handled all the subtleties already :)