If you have a physical disc but no internet connection, you cannot download the pack via Steam. You will need to source the en_english folder from a friend who has the full version. Place it in: C:\Program Files (x86)\Steam\steamapps\common\Call of Duty Ghosts\zone\
For console players, language packs are managed through the system menu: callofdutyghostsenglishlanguagepack
Quick install — Consoles