Like virtually all modern software, Buzzword adheres to the Unicode standard, where characters are defined with 16 bits, resulting in a total of over 65,000 possible characters.
Buzzword must use something called "embedded fonts".
MS Office has a good UI of setting supported "editing_languages" in their office language settings tool. It has a list of languages that can be edited in the document.
It has been more than 3 years after this thread has been started, and as far as I can see international characters are still not supported. I find it hard to believe such a think would take this long to support. So I would like to update the question: are you still planning to support internartional characters?