Apostrophe followed by vowel automatically replaced by accented vowel

Dear Apple Community,

My Mac (iMac running Catalina 10.15.3) automatically replaces apostrophes that are followed with a vowel with an accented vowel.

This is not a problem when writing in English (as apostrophes are always followed by a consonant), but I live in France and about half of the stuff I write is in French. So, if I try to write c'est, it will give me cést. And I don't know how to turn this off

Heeeelp

Thanks!

ps: I'm using a US keyboard