Language packs do not require a new serial number. Your existing English license works for the PT-BR interface. However, note that by Autodesk. Installing it on Windows 10/11 may require the ADSKLICENSE compatibility fix.
If you cannot locate a trustworthy copy of the language pack, consider migrating to a newer AutoCAD version that natively supports Brazilian Portuguese. However, for the millions of .dwg files created between 2011 and 2015, AutoCAD 2012 + PT-BR language pack still represents a stable, productive environment. autocad 2012 language pack pt br
Once you've downloaded the Language Pack, follow these steps to install it: Language packs do not require a new serial number