AutoCAD commands are in language packs. For example:
Ensure AutoCAD 2021 is fully installed and closed before beginning. Language Pack Autocad 2021
If you frequently switch languages, download the from Autodesk Account. It includes all languages in one installer (approx. 12–15 GB). You choose language at installation time. AutoCAD commands are in language packs
Language Packs are add-on installers that provide a localized user interface (UI) and documentation for AutoCAD. They do not replace the core software; rather, they add specific language layers. Language Pack Autocad 2021
: Language packs for "Vanilla" AutoCAD may not automatically localize specialized toolsets (like AutoCAD Architecture or Mechanical). Those often require their own specific language downloads.
If AutoCAD 2021 is already installed in English (or another language) and you wish to switch: