Wikipedia:Unicode
Wikipedia uses Unicode (specifically utf-8) to encode text in articles and article titles. Unicode is a successor of encodings like latin-1, which only handles european languages (and some others). With Unicode, Wikipedia has support for a large part of the world's scripts.
Browser support
Most modern browsers support Unicode, and most users will not find any problems to edit Wikipedia.
For older browsers, MediaWiki, the Wikipedia software, serves the wikitext in a safe mode upon editing. Unicode characters are represented in hexidecimal, looking like Ӓ