I’m sorry, you don’t get to maul the pronunciation of loan words and then correct people when they use the correct pronunciation. The word comes from the french cache/casher which is pronounced exactly cash-eh. Where do you think the -e comes from?
cacher does, but cache as in “cache-toi !” (go hide!) and “je me cache” (I’m hiding) are pronounced “cash”.
Besides, “correct” pronunciation in a different language is pretty meaningless. The word may have come from French but we’re speaking English, not French.
Also, it might not be a loan word so much as a legacy-of-foreigners-taking-over word (c.f. the Normand invasion of Britain), which doesn’t tend to help the language’s users care about respecting the “original” pronunciation. I’m not certain when exactly cachet entered English.
From the Mirriam-Webster website:
A cache is a group of things that are hidden, and is pronounced like “cash.” Cachet can mean “prestige,” “medicine to be swallowed,” or “an official seal,” and is pronounced “cash-ay.”
Cache and cachet share a common French root – the verb cacher (“to hide”), which is pronounced \cash-AY\ – but they are pronounced differently and mean two different things
In English, yes. My point is that cache/r/t is the root of both words, the pronunciation changed in english which often happens with loan words, and it certainly is OK to use the local pronunciation – but correcting someone who uses the correct pronunciation of that word, with self-righteous indignation even, is very silly behavior.
“But we’ve been pronouncing it wrong for 300 years!”
If we said every loan word the way they were originally pronounced in their various native languages then English wouldn’t exist.