I was intrigued about where Visual Studio was getting the languages to fill the Language combobox in the Tools, Options dialog, Environment, International Settings section. After some investigation I discovered that the list is not stored in the registry or in some file. Visual Studio just scans the subfolders of the C:\Program Files\Microsoft Visual Studio <version>\Common7\IDE folder and checks which ones are LCID numbers!
So, you can copy the 1033 folder (which is English) and paste it as 3082 (which is Spanish) and you get the Spanish language in the combobox. Of course the user interface and everything else is in English because you didn’t get really the Spanish resources (that would require to install the full Spanish version of Visual Studio) but it is useful to test if the managed satellite dll for custom pictures will be loaded when the IDE is not in English (the problem that I am investigating now) without installing a full localized version (and its service pack and its security patches…)