Anyone would tell you that being bilingual, or even trilingual has its advantages. A physicist would tell you that celsius has its shortcomings -- after all, where on that scale does all motion stop? In Kelvin, it's at 0 degrees. How does an Astronomical Unit compare to metric? A kilometer is an ungodly non-decimal number when compared to that scale. Any system of measure, if examined, will come up short.
But because you mentioned it, the US military still uses imperial measure for a lot of its weapons. Yes, the M16/M4 is "5.56 mm" but their legendary sidearm (still in use by certain units) is the .45 ACP, which is .45 of 1 inch in diameter. Their preferred shotgun is chambered in 12 gauge, and "gauge" is defined as the number of lead balls of the diameter of the barrel that makes up one pound. Hardly metric.
Imperial measure was based on the human. 0 degrees is about as cold as you'd want to be when you're outside, and if it's 100 out, you're looking for some shade and a cold drink. (You've also got a fever at that temperature. In metric, that's a hair north of 37 and 3/4 degrees, which isn't as memorable as 100.) I'm happy with people drinking a pint of beer at a sitting, but a liter? That's asking for trouble.
Your argument about languages "not being the same" as measurements falls short. Can you imagine how much easier it would be for global trade to be conducted if everyone knew what the other was saying? Can you imagine what the United Nations would be like if no-one relied on interpreters? (And know that "interpreter" means "subject to interpretation", which inevitably means there will be something lost in translation.) What about healthcare? A Chinese person being attended to in an emergency could just say "this hurts" instead of leaving it to the medical providers guessing what's wrong. There would be so much more common understanding, instead of all this approximate guesswork. We could standardize on the same 26 letter alphabet, without all those pesky special characters -- get rid of the tilde, all those different accent marks the French insist on using, and to hell with Cyrillic and Chinese. (Heck, if you want to read a Chinese newspaper, you better know about eight thousand characters. Kids spend years just learning how to write all those different characters, instead of just learning 26 letters and 39 phonemes. That's not efficiency, that's insanity!)
English is already one of only five official UN languages, and all aircraft pilots are required (by international treaty) to be fluent in English -- it's the only language commonly spoken in every air traffic control center around the world. It's also the lingua franca of much of the world's commerce.
We never hear of a mass exodus of Americans jumping over the Rio Grande into Mexico. It's the Mexicans and all the other Spanish speakers coming up into America, and when in Rome, right? So it makes sense for everyone in Central and South America to stop speaking Spanish or Brazilian, and start speaking English, like everyone else who's successful. After all, if you want to do business in America, you should use a unified language, to paraphrase your own argument, right?
By your own logic, there are more reasons for everyone to give up their mother tongue in favor of English. The military uses it, as does every science teacher of any class you've ever taken, and it's already commonplace for the entire populace of the US and most of Canada. (And even most of the Quebecois speak English as well as French, although they can't stand to admit it.)
Feel sickened yet? Like you showed up at a Trump rally, wearing a bright red MAGA hat? Try this, it'll make you feel more tolerant:
Please, go on using whatever scale you prefer. I won't stop you. But as a courtesy to all under the heavens, make peace with the fact that some people speak other languages, and that goes for how they measure things, too.