So you have downloaded the english_pack_mw3.zip file from a trusted source. Here is how to install it correctly.
// Download language pack DownloadLanguagePack(); Cod Mw3 English Language Pack Download --BEST
: Navigate to the Call of Duty application on your home screen, press the Options button, and select "Manage Game Content." Look for "Language Data" to find the English pack for download. So you have downloaded the english_pack_mw3