It wants me to translate this as "I need some red t-shirts". Surely then the original Spanish sentence should have been "Necesito algunas camisas rojas."? Something strange going on here?
The thing that's going on is, that they want you to know the meaning of English 'a'/'an' ; you see, in Spanish 'alguna' could be just that.
It rejected "i need some red tee shirt".
It said "You used the singular "shirt" here, instead of the plural "shirts".
I need some red tee-shirts."
I was using "some" in the same way as "some enchanted evening" -- a literal translation of "alguna". It tried to turn it into a plural!
Reported 24 May 2018.
So, it looks like both "I need a red t-shirt" and "I need some red t-shirts" are both accepted.
I think it's weird that they recommend the plural. But "I need any red shirt" is also accepted, which makes sense. But "I need some red shirt" should work too
I got: "You used the wrong word. I need one red t-shirt."
They just can't get anything right this morning, that's three in a row they've messed up. I need one decent Spanish learning program. DL now disappoints at every turn.
You have one decent learning program in DL. It was never meant to be the total answer or used without supplemental sources – dictionaries, for example. As far as "messing up" here is concerned (they have not), take a look at the various uses of "alguna" in the "Phrases" section here:
I did take a look at your link. And I saw that they indeed messed up. My answer was in there, so they should have accepted.
You don't say what your answer was, so I can't speak to that, but with regard to "I need one (or a or any) red t-shirt," they absolutely did not "mess up" insofar as those are renderings for "alguna" they are trying to point out for us. As for not accepting a given plausible translation, yes, of course, there are instances of such omissions, but the lack of all possible renderings does not, ipso facto, equate to a "mess-up." If you think your answer "should" have been accepted, report it. DL does, in fact, work to minimize such omissions.