In SharePoint there are already a lot of translated strings, that you can find in the resx files in the folder C:\Program Files\Common Files\microsoft shared\Web Server Extensions\12\Resources.
You can incorporate them in your resource files in the form $Resources:StringID;. For example you can use:
To access them from C# code, you can use the method SPUtility.GetLocalizedString.
For example, to retrieve the name of the Document content type, it is possible to use the following line:
string documentCTname = SPUtility.GetLocalizedString("$Resources:Document", "core", web.Language);