This article discusses business papers XII-XIII century from the city of Augsburg, which is located in the south of Germany. The norm of the modern German language went through several stages of formation before acquiring a unified standard and becoming the so-called Standardsprache. The city of Augsburg belongs to the East Bavarian dialect region and is located on the border of Bavaria and Swabia. Analysis of the written language of documents of the XII-XIII century provided information on the interaction of the features of both dialects (Bavarian and Swabian). In this study, 5 documents related to various taxes were considered, which indicate that they were written in Augsburg, as well as 3 documents in the Augsburg monastery. It is important that for the documents considered there is no characteristic sequence in writing, that is, we are talking about the absence of a spelling norm. Confirmation of this fact is also given in the article with examples from the materials studied. The study showed the presence of similar characteristics in all studied, which indicates their undoubted linguistic kinship. Despite this, there are also features that are characteristic exclusively for the southwestern part of Germany and separately for the southeast. An analysis of the German southern dialects makes it possible to trace the development trend of the German language in its holy language in a period that is closely connected with the history of the German people. The processes of synergy between dialects within the framework of one language are considered, which draws attention to the beginning of the formation of the first national language, and subsequently the national one. The study revealed that Augsburg became a kind of conductor of the Bavarian dialect in the eastern part of the Swabian dialect. The isoglosses studied (phonetic, morphological, lexical) showed that these dialects can be combined linguistically as southern and considered a feature of the Germanic (Yerminon) range. Despite some linguistic differences, a relative unity of linguistic traditions is noted, indicating a sufficient proximity of the dialects of the southwestern and southeastern parts of Germany in the XII-XIII centuries.