If I type the name of a quest IN ENGLISH in the Google search engine, the first result I get is that very same quest translated in French on Wowhead.
Every time I visit the website, I need to manually put it in English.
Go into your browser settings and change the primary language from French to English. WoWhead may be detecting your browsers primary language and putting the page to it accordingly.
Step 3: Make sure English is specified as the preferred language in your browser’s preferences. In Firefox you can set that via the three-bar menu and Preferences, or by typing about:preferences into the location field.
NB: Preferences you set in Steps 1 and 2 are only saved if you are signed into Google.