It's a mistake.
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The english translation is "You drink these milk."
How do I tell the difference between these (diese) and this (diese)?
diese (plural) = these; e.g. diese Frauen lachen
diese (singular, fem.) = this; e.g. diese Frau lacht
So how do you say 'You are drinking that milk'? It didn't accept it, and I'm confused by this and that.
Actually, I believe that "that" specifically would be „jener“. Since Milch is feminine, you would say „jene Milch“, but it is my understanding that „diese“ can be used for either "this" or "that." The distinction between the two in German is not as salient as in English.
Actually, I believe that "that" specifically would be „jener“.
Sort of true, but a better comparison would be jene Milch = "yon milk".
Never heard of "yon"? Nor do most German speakers use jene in daily conversation. They're both more theoretical words than practical ones.
In practice, "that" is der/die/das -- which can also be "this".
dieser/diese/dieses is "this" -- it's not generally possible to translate it as "that".