It's just plain wrong to use "invent" that way in English. He designed JavaScript, he didn't "invent" it. Designing and inventing are two very different activities.
You wouldn't invent a specific language, but maybe the concept of "programming language" itself or specific language features. Lovelace invented the program, Zuse invented he programming language, and someone invented classes (probably Scandinavian) and first-order functions (probably a mathematician).
invent: create or design (something that has not existed before); be the originator of.
So invent and design are near synonyms. There are subtle differences, of course. For example, I don't think it would be right to accuse you of designing the distinction you're making here. ;)
Just because create and design are not synonyms doesn't make invent and create synonyms. Invented can be used as a pretentious form of create I guess, but it just makes the subject look like a tool. Edison invented the light bulb is ok, there weren't any economically viable light bulbs before. Eich invented JavaScript just makes Eich look bad though, there were plenty of PLs existing before that Eich borrowed from in his design.
I do agree that "inventor" is much stronger than "creator" but in the case of something as huge as JavaScript itself, I think he deserves it :)