> One of Charlemagne’s last descendants to be king of West Francia – the predecessor kingdom to France – grew up in the court of his uncle, King Æthelstan of Wessex in the tenth century.
Just to put things in perspective, Franks were a Germanic people and were much more culturally affine to the Anglo-Saxons.
Charlemagne didn't speak "French" so it's no surprise Louis IV didn't either.
The Latin substrate in the territory of modern France was so strong that it gradually took over the Germanic ruling class over centuries. Old French evolved during this time before the norman conquest.
Because the people of the Mediterranean were as imprecise as westerners are when referring to other people. They called "franks" any people in the west that didn't speak Greek. In the same way as many today call arabs any people that are Muslim even if thet are Turks or Iranians
> Latin substrate in the territory of modern France was so strong that it gradually took over the Germanic ruling class over centuries
Good place to point out that those Germanic speakers had a major impact on French, and to this day it is by far the most heavily influenced by Germanic, of all the languages descended from Latin.
For example: attaquer (attack). craquer (crack), affreux (fright), hautesse (height), saisir (seize), taper (tap), trier (tear). (I've given English cognates in parentheses, not translations -- "taper" means more like "to slap".)
In fact, Germanic borrowings are around 10 - 20% of French vocabulary.
Some words in English have actually cycled between the Germanic and Romance branches multiple times because of this. For example, Old French had a verb, something like "warder". Probably borrowed from Frankish. English borrowed "warden" from Norman French. Later, sound change in French shifted /w/ to a /gw/ sound, so warder -> guarder. English borrowed the word again, giving us "guardian". In this particular case, English also kept the original fully Germanic form - "warder" (noun).
> Franks were a Germanic people and were much more culturally affine to the Anglo-Saxons.
It very much depends on what you mean by Franks. As with everything in History, terms themselves have a history that must be understood.
Clovis-era Franks were a Germanic people. Later in the Merovingian era not so clearly, as Germanity wasn't a defining characteristic of the Franks as a people and Germanic origins were seemingly forgotten.
The push East under the later Merovingians and early Carolingians likely produced more Germanic-speaking Franks than there were before.
As for Charlemagne, while he couldn't indeed speak a language that didn't exist yet (French), considering the area his family was based around as well as his constraints and style of government, it would be surprising if he wasn't bilingual in Gallo-Romance and High German. Bilingualism is heavily implied throughout the Carolingian era in a lot of the written source, and explicit by the end.
High German didn't exist yet, though. The High German sound shift hadn't happened yet.
At that time all the West Germanic dialects would have been closer to what we call "Low" Germanic now; Dutch, Low Saxon, Frisian, etc. Harder consonants where German now has softer ones.
And I imagine it was probably easier for them to muddle through mutually understanding each other back then.
But yes, in addition to Gallo-Romance, he probably spoke something similar to Old Low Franconian, which eventually became Dutch.
The Frankish nobility would have been a minority in a land which was majority Romance speaking (Gaulish having unfortunately died out out by then). And at a certain point they were very interested in emulating and continuing the lineage of the western Roman empire, explicitly taking up late Roman styles and practices. Adopting Latin and Gallo-Romance speech would be just part of this.
Happened with the Goths in Spain as well.
It's interesting to compare to Anglo-Saxon England where this did not happen and the native Brittonic speech as well as late Romano-British Latin was wiped out.
Just to put things in perspective, Franks were a Germanic people and were much more culturally affine to the Anglo-Saxons.
Charlemagne didn't speak "French" so it's no surprise Louis IV didn't either.
The Latin substrate in the territory of modern France was so strong that it gradually took over the Germanic ruling class over centuries. Old French evolved during this time before the norman conquest.