You are using the Steam version of FM 2010. Fix: Steam’s DRM sometimes locks the languages folder. Go to the Steam directory: Steam/steamapps/common/Football Manager 2010/data/languages . Apply the pack there, not in Program Files.
Copy the desired language file (e.g., english.ltc , spanish.ltc ) into this languages folder.
First, let’s clarify terminology. Unlike modern FMs which support dozens of languages natively via Steam, Football Manager 2010 was relatively restricted. Depending on your regional disk or digital download, you were locked into perhaps two or three languages.