An "Archicad Language Pack" typically refers to two distinct things:

: Specific library packages ( .libpack ) that contain translated object names and parameters for the standard Archicad library. Why You Can't Simply "Change" Languages

Unable to change the language in Archicad? - Graphisoft Support Site

If you need Archicad in a different language than your current installation, follow these steps:

: Comprehensive translations of the entire interface, including menus, dialog boxes, documentation, and help files.

In Archicad, the language is deeply embedded into the program structure. You cannot change the interface from Russian to English or Spanish to German through a settings menu. To use the software in a different language, you must install the specific localized version from the Graphisoft Downloads page . How to Install a New Language Version

The Complete Guide to Archicad Language Packs and Localization