If you want to change the language of user environment in the Inventor Content Center (CC), you can just modify the loading control file for this add-in.
Use Notepad to add (or edit) a line in the file Autodesk.ContentCenter.Inventor.addin stored in the folder C:\Users\YOURUSERNAME\AppData\Roaming\Autodesk\Inventor 2013\Addins\ as:
<Language _OVERRIDDEN_="ADDED" CCLanguageOverride="de-DE"></Language>
<Language _OVERRIDDEN_="ADDED" CCLanguageOverride="en-US"></Language>
The language setting can be switched to any value supported in all localized versions of Autodesk Inventor, so you can choose also more exotic languages like cs-CZ (Czech), hu-HU (Hungarian) or zh-CN (Chinese):