All files are in UTF-8. But really most files are pure ASCII:
ASCII: core templates, almost all source and test files living in bin/, lib/ and t/.
UTF-8: localized strings in po/, localized conference templates,
conferences' act.ini, a couple of source files which
The databases are in UTF-8.
All output (web, email) is in UTF-8.
Conference templates, static pages and .ini files are in UTF-8