Of interest is that while the Germanics themselves, at least in High German, preferred the term diutisc for themselves they labeled the foreigners at the edge of their marches (frontiers) as walesc.
At least in English now, for some but not all call themselves other names in their own tongues, the Welsh in the UK (Cymry in their own tongue), the Walloons in Belgium (Walons in their own tongue), and the Vlachs of Eastern Europe (Roumanian in their own tongue) all were originally just waslesc, "foreigners", to the Germanic people. The border between the Flemish (German-speakers) and Waloons (French-speakers) in Belgium has been a stable dividing line between these two tongues and ethnic groups for a very long time BTW.
@ questionmark since you could not answer the questions previously asked or offer proper proof for what you claimed here is another chance in another matter: if you can find older sources than this in a vernacular Germanic tongue (and not Latin) for what they called their language, their lands, or themselves, then please offer it.
For now I leave you the following:
The Annolied (Song of Anno) was written around 1100 in Early Middle High German. Again, if you can, find anything written by the Germanics in their own tongue that offers a different naming convention...
First will be the Germanic venacular of the era followed by an English translation.
[English link] [German link]
Anybody who knows a little about German literature would know that the above is the fifth oldest writing fragment in any High German dialect, the oldest being the Prayer of Wessobrunn (800 A.D.), so the task would be near impossible, would it not? Kind of like asking who came before Adam? And we are again 200 years away from our time frame.
The previous works are about the three wise guys (a theater play, 1080), the Memento Mori (1070) and the Ezzo Song (that deals mostly with Biblical motives, 1063). What you need is records and letters. And as hint: those were mostly written by the chaplains as they were probably the only ones in the court capable of writing at all. The oldest charter written in German, and not Latin dates from the 13th century, so that does not help either very much... but documents in Latin where the words were translated and showing the original do help.
But this may help you as reference: The translation of Latin school books for use in German Cloister Schools was called the Teutonicus (~950 A.D.), not the Germanicus, and certainly not the Diutsce.