You need a localization (mui and stuff) file for Spanish... its also apply to chinese, russian, german, etc...
if you take a look at the kitchen, you'll hv 0409 (English US) MUI/Localization files, so in order to make another languange rom/kitchen u need other languange mui... its simple... but you need the mui's and localization file... check ms site for windows mobile MUI/localization..
check this link for start:
http://msdn2.microsoft.com/en-us/library/ms904030.aspx