Historically, different language versions used entirely different "Monolith Libraries," which made collaboration across regions difficult.
: You must download and install the specific language version you want to use. Each localized version (e.g., German, French, US English) is a standalone installer. License Compatibility
For working with Archicad language packs, the most helpful documentation and "papers" focus on the introduction of Library Packages (libpacks) and the MUI Resource Technology used for add-ons. Essential Technical Guides How to Create Multi-Language Add-Ons
The interface will match the software version you are currently using. If you open a French file in Japanese Archicad, your menus will be in Japanese.