In 842 in the city of Strasbourg, the grandsons of Charlemagne, Charles the Bald and Ludwig or Louis the German, swore oaths against their brother Lothar. What is interesting about these declarations is that both men spoke in the vernacular language of their respective realms: lingua romana of the western Franks (present-day French) for Charles and lingua teudisca of the eastern Franks (present-day German) for Ludwig. Since he was the older brother, Ludwig swore first in his brother's language:

Pro deo amur et pro Christian poblo et nostro commun salvament, d'ist di in avant, in quant deus savir et podir me dunat, si salvara eio cist meon fradre Karlo et in aiudha et in cadhuna cosa, si cum om per dreit son fradre salvar dist, in o quid il mi altresi fazet, et ab Ludher nul plaid numquam prindrai, qui meon vol...