Yes, but not all programs will work on other OSes. Microsoft Applocale allows you to run software designed for other language versions of the OS (for example, running a Japanese or Thai program on an English version of Windows). Some programs aren't made to work with language packs, and therefore can't display their characters properly on an English OS. Instead, you get a series of boxes or question marks.
There have actually been a lot of cross-compatibility improvements since early versions of Windows. The 9x line (95, 98, Me) had very little support for cross-compatibility and would almost never run other language programs properly. For XP and the NT line, AppLocale is a temporary solution, but they suggest if you really need to run things in other languages all the time to get a version of Windows designed for that language.