« Melon d'eau » ? For watermelon? I thought it was a joke, but well, Wikipedia mentions it: « La pastèque [...], parfois appelée melon d'eau » (https://fr.wikipedia.org/wiki/Past%C3%A8que)
Everyone says « pastèque » in mainland France, where I've lived for over 40 years.
I've never seen melon d'eau and I doubt anyone will understand it unless they know the English word.
This is a remnant of British colonization. French-speaking population didn't know any English, so you have a lot of these literal translations.
I've heard "flour" uttered with the French pronounciation (fl-oo-r, instead of homonym of "flower") in New-Brunswick. I was floored. Took me a while to figure out what they meant.
Clearly, this originates from non-English speakers reading "flour" on a sign and just running with it.
Also, consider that the British conquest happened before watermelon was highly prevalent in France or North-America. It's unsurprising to see terminology diverge in this case.
