Why do we use non-English words?

We resort to foreign words for a number of psychologically interesting reasons. A lot of them, I’d argue, are rooted in the middle class aversion to bluntness or crudeness. When what we’re saying has an underlying tone that may cause embarrassment to either the speaker or listener, we borrow from Latin or modern European languages (often French) to give a veneer of refinement, glossing over what’s crass, base, or stark.

Source: Strictly entre nous: why do we use non-English words? – OxfordWords blog

For example, on the use of entre nous: “I want to gossip but gossiping is common so I’m going to get away with it by using the pretentious French phrase for it.”