Hi, this is a popular question with complex answers :) Pull up a comfy chair and check out these threads:

• How "French" were the Franks? (plus some bonus questions) featuring /u/Dux89 and /u/Angharat

• The Latinisation of the Germanic tribes who invaded the Western Roman Empire: how and why? featuring /u/GeorgiusFlorentius and /u/jutebox

• How did the Franks go from axe-hurling, Germanic-speaking pagan tribesmen to the God-fearing, Gallo-Romance speaking knights in shining armor of Charlemagne's time?, which I've included mostly for the unforgettable title, featuring /u/haimoofauxerre and /u/Fdurke

• Why did the Franks end up speaking a Romance language while the other Germanic tribes did not? featuring /u/SCDareDaemon and several others

• How did the Franks end up speaking French? featuring /u/alriclofgar

• Who was the first Frankish ruler to speak French instead of German (Old Frankish)

• If the Franks were a Germanic people how did they come to speak French, a Latin/Romantic Language?

So. These posts have all been archived, so if you have follow-up questions for any of the users therein, just ask them here and tag their username to notify them.

I have been trying to figure this out, but I have found many contesting answers