Core files are now UTF-8
On our move in the direction to full UTF-8 compatibility, the core team decided to convert all PHP source files to UTF-8. This mainly affects comments and author names (e.g. Kasper Skårhøj).
If you work with the source of the core (as a core contributor), Steffen Kamper has written a small article on buzz on how you change your project settings to support the new default.