> French person here : no differences, we pronounce them all é and we don't care.

That is very far from the truth, and unhelpful. Yes, some people have accents, but it’s not because you cannot hear the difference (or at least claim you cannot) that it does not exist. Out of curiosity, how do you pronounce "il a fermé la fenêtre"?

For non-French people: there are accents in which é and è are most of the time very similar, particularly in the South. They are very proud of it somehow. I am all for regional accents, but claiming that your particular pronunciation is the one true way is ridiculous.