I assume that you want the same program to be available with ther option of different languages. You need to know that Pocket PCs are Unicode based, even the OS while on the desktop .NET is also Unicode even if the underlying OS is not. What this means is that you don't have to do any character code conversion as the Unicode character set includes all languages.
I would suggest that rather than keeping strings in the program they are read from a UTF8 format text file at runtime. You may need to extend this to the text in lables and on buttons etc.
You need to get the Unicode strings in the correct language in the UTF8 files. This can be a problem as keyboards are set to a specific language so that even a Unicode aware program, like Notepad in XP and Vista, can only easily generate files in the language that the system is set to. You may need to generate each file on a PC or device set to the appropriate language.
Naturally each device will need the system set to the required language to get the correct font for each language.