Eh... coffee glasses would be taken more-so to mean "glasses used for coffee" rather than "glasses filled with coffee".
You could use the same word or add in a word to remove the ambiguity like chứa (to hold/to contain). Ly/cốc (chứa) cà phê, or something like Ly/cốc (dùng để) uống cà phê meaning "glass used to drink coffee".
How would I know that this sentence is plural? As in "cups of coffee" vs "cup of coffee"? I think I'm missing something
When I hear glasses I think for juice or water. Coffee is in mugs and cups. "cup(s) of coffee"
Yeah, this question is dumb. The English translation makes no sense (from the POV of a native, University-educated American English speaker). And it's actually mildly dangerous! See below ;)
If the intent of this question is to specify that He sells vessels (cups, glasses, mugs) CONTAINING coffee right now, for YOUR immediate consumption ], in English, we'd say "He sells cups of coffee".
This does not make an assumption about the vessel itself, "cup" being used in an abstract sense; the vessel containing coffee is not relevant to the sentence. In general, this will be a disposable paper or foam cup for takeaway, or a mug at a restaurant which will not be removed from the premises; that would be stealing, so apply your own moral judgment here!
Continuing with the intent of selling a drink-able unit of coffee, selling Mugs of Coffee makes sense when the type of vessel matters; perhaps Cup is too vague because the situation requires specificity. For example, to differentiate between a disposable cup and a non-disposable mug in situations where portability or environmental concerns are at hand.
Continuing along the "a cup of coffee for your consumption right now", using "Glass Mug" might make sense in a given context if the speaker requires an adjective to describe the Mug in further detail.
For example "He sells glass mugs of coffee" could set him apart from the guy next door, who sells coffee in porcelain mugs. Rarely an important distinction, but perhaps the speaker is a coffee snob and prefers coffee in glassware. Very uncommon, but correct English.
Selling Mugs FOR Coffee implies he's ONLY selling the mug (no coffee included). But the above VN sentence does not contain (or seem to imply) the word "FOR".
I believe the intent here is to specify a vessel full of liquid, so I would think something like "tách" (a usually-round hollow container to hold liquid for drinking, often with a handle) would make more sense than "ly".
So, why dangerous?
We would -never- use the word Glasses (w/o a further modifier) to describe something you put coffee in (mainly because a normal glass would likely shatter under the thermal shock of steaming hot coffee being poured in).
In this case, you'd have extremely hot coffee splattering everywhere; enough to cause 2nd-degree burns, containing shards of heated glass in it (enough to slice your skin and exacerbate the burns substantially). This will require a trip to the hospital at very least, and possibly long-term nerve damage to your hands. And boys...let's hope that it doesn't land on your lap!
That's why we use....MUGS, glass or otherwise, mugs are specifically designed NOT to shatter under sudden thermal stress; that is basically THE definition of "mug"; a vessel for holding very hot liquids safely.
Just trying to paint the substantial contrast between the intent of the question and a native speaker's interpretation with an over-the-top explanation ;)
Actually there's a very popular drink sold in Vietnam called "cà phê sữa đá" translated as "coffee with milk and ice". Its actually really nice as its made with condensed milk and is incredibly tatsty. The hot filter cofee is very debse and of a small liquid volume. Likewise it is dripped slowly into a glass with ice. This slow speed prevents any risk if thermal fracture.
Additionally for normal coffee, its perfectly feasible to put hot liquid in glass as long as the glass is treated properly - such as being annealed to enlargen the crystal grains, making it less brittle and hence make it less susceptible to thermal expansion shock. One such product line would be that of Pyrex glassware.
However, please remember this is a language learning app, and such a small technicality is insignificant. The translation is technically, semantically and grammatically correct and teaches a new use of a previous word. So its not that big if an issue imo.