The Austro-Bavarian language has its origins in the Germanic tribe known as the Bavarii , who established a tribal duchy , which covered much of what is today Bavaria and some of Austria in the early Middle Ages and was eventually subdued by Charlemagne . The Austro-Bavarian regiolect has its origins in the Germanic tribe known as the Bavarii , who established a tribal duchy , which covered much of what is today Bavaria and some of Austria in the early Middle Ages and was eventually subdued by Charlemagne .