Many people have heard from time to time words from other languages, where after hearing the word, they’re told that there’s no word for it in English.
Yet, according to the Guiness Book of World Records, English has a vocabulary of over 600,000 words (including technical terms.)
Now, with a vocabulary of over 600,000 words, shouldn’t there be an English word for almost any word from any other language?
Surely not a GQ topic…
but…
the strength of English is in its mongrel status. It can easily absorb any word thrown at it, and continually acknowledges new ones, be they ‘email’ or ‘pukka’ or ‘smorgasbord’. If there’s a need for a new word, and another language can provide an appropriate word, then English will often take that word on as its own.
And to continue my ramblings in a way that responds to the OP - if there’s a word available, then use it. Hopefully, if it is meaningful, it’s possible for it to very gradually cross languages.
The OP implies that there are only 600,000 possible concepts in the entire universe. This is not a very good assumption.
To summarize what I think Gman said, if there’s no word for it in English, the word in question becomes part of the English language. Gestalt is an example that comes to mind.
As does exemplum (Latin, obviously), kuam (Norse), and to (probably Anglo Saxon). Mind you, ‘mind’ is problematic, althoug probably at least of Germanic descent.
It’s terribly puzzling why English is so huge yet still not complete…
One fundamental problem is that there isn’t a one-to-one mapping between the words of different languages.
If you have to describe a concept, you can usually do it in English, but there is a good chance that there is no single word that captures exactly the same nuances of meaning as a foreign word because the “boundaries” between the meanings are different.
Also, although English certainly has an enormous number of words, those counts are a bit problematic. Deciding what is a word of its own is a lot harder than it seems, even more so in languages that make more use of compound words (like German, but also any others.)
kellner,
lexical semanticist in training 
FWIW, I had a violin teacher when I was a kid, who was English but fluent in Swedish, and would frequently write Swedish words on the page where they made more sense than an attempt at a translation. I’ve no memory of what they were, but if I go and look at the music, I know what was being said.
There are any number of examples of words “missing” from English. Some are concepts from other cultures which English merely uses a loanword for: schadenfreude, for example. Others are examples of distinctions other languages make which English doesn’t: say, the difference between French savoir and connaître. Finally, there are even uses which are just missing; “Proper” English has no transitive verb to describe sexual act AFAIK.
I’m not a language expert, but there are many words in other languages that are hard to translate into English. That’s not to say that there isn’t an English word that is roughly similar. The problem is that there are subtleties and context that get lost in the translation. Try comparing the Hebrew text of the Torah to an English translation of the same.
I’m sure there’s many words missing from many ‘proper’ languages.
It’s because English lacks a certain, je ne sais quoi
An anglicised phrase, if ever I heard one 
My French is very rusty, but IIRC savoir means “to know” and connaître means “to understand”; a distinction that IS part of English.
I must be missing something.
No. Roughly speaking, savoir means to know a fact; connaître means to know a person, or be familiar with a thing. Je sais que Montréal se situe au Québec (I know that Montreal is in Quebec); je connais Montréal (I know Montreal). (Understand is comprendre.)
And if you think that’s tricky, try ser and estar in Spanish. Caused me no end of grief.
And that’s without even going into the prepositions.
I think my favorite example of this was a Cherokee medicine man who once said to me, “You know that feeling you get when you wake up, snuggled in your sleeping bag inside a tent, and it’s just the beginning of autumn, so the air is crisp and cool and you just feel so alive, and you get up, stamping your feet against the chill, open your tent to the sky and realize that last night you pitched your tent (in the dark) on a hilltop, and as you look up through the trees, you see a single hawk circling above you, and then you turn around and look down over a valley of great beauty, all reds and oranges and the rush of your blood just swells up inside you, and your heart feels like it’s going to burst with the indescribable love of all creation?”
“Um, yeah, I guess,” I said.
He smiled. “We have a word for that.”
“To understand” is comprendre (Comprenez vous?). German also has the distinction between knowing someone and knowing how to do something (I took a german course out of interest a while ago, but I’m not about to embarass myself by misremembering the words )
The French word chez is a little tricky to translate into a single word. It’s “the home of”. You could translate Chez Helen as “Helen’s place”, except that you end up having to use the possessive in English, which you wouldn’t in French.
You’re proving the point made earlier. ‘Chez’ has been adopted in English, fulfiling the ambiguous roles you idetify.
Conversely, French has no single word for “home,” to the extent that there was once an abortive attempt to borrow the English word home. The word foyer is close (as in “protégéra nos foyers et nos droits”), but the meaning is closer to “household,” and you can’t really use it to mean “where the heart is,” as it were. (It also means “fireplace.”)
One of the ways I’ve seen “home” translated, in fact, is “chez soi” (at one’s own place.) If you’re wondering, Star Trek IV was Retour sur terre.
Should have clarified, that’s as a noun (“son chez-soi” = “his at-one’s-own-place”).