According to Oxford Dictionary, tea is uncountable. However, there's a countable form i.e. a cup of tea. Is it natural to leave out a cup of and just say two teas please, for example?
I saw a sentence that used plural teas from Du*lingo:
These teas, do you want them?
Is that sentence OK grammatically?
Yes, that's perfectly grammatical since the context is clear.
When you encounter the question of countable versus uncountable, it's useful to think in terms of the substance (uncountable) versus a specific variety or quantity of the substance (countable). Consider:
Tea is good for you (uncountable - referring to the substance)
A tea in the morning is a great way to start your day (countable - referring to a serving/quantity of the substance i.e. a (cup of) tea
This is quite common for food/drinks. (Beer, wine, steak - there are a lot)
Remember, where the context is clear (i.e. ordering food/drink), the countable form without the specific serving vessel or quantity is often used:
Two beers, please
A water with ice, please
These phrases: "n teas", "n beers" are short forms of "n cups of tea", "n bottles of beers" respectively.
It might be well understood when you say that. When you want to write it as such, it is incorrect (at least grammatically).
This use is normal in British English. I believe it is much less common in American English.
Lynne Murphy says in The Prodigal Tongue, chapter 6:
[Something else] echoes the established British hot-drink patterm. Americans meet other Americans for coffee. If they want to count how many coffees, they generally add a countable noun, like cup: two cups of coffee. Brits might meet for a coffee.
