That would be the phrase I would use (as a native). So you're right. The thing is, koreans learn "is/am ~ing" should be translated to "~는 중이다" or "~고 있다". These expressions show that the action itself is not finished, just what ~ing does. Duolingo must have used "sleeps" because the korean sentence did not use "~하고 있다" nor "~하는 중이다".
Shortly put, you are absolutely right, but I can understand why a machine would mistake it.
(1) "Always" in English can be used either as an adverb of frequency (= habitually) or as an adverb of manner (= continuously)
As adverb of frequency, always = 항상 (regularly, habitually).
As adverb of manner, always = 계속 (continuously, without interruption)
제 햄스터가 항상 자요 = my hamster always sleeps (=> a habit)
제 햄스터가 계속 자요 = My hamster keeps on sleeping/ is always sleeping (=> sleeping non-stop, an uninterrupted state)
(2) As for Korean present progressive ( ~는 중이다" or "~고 있다" ), it is only used to put an emphasis on an action in process right at the moment when the statement is made.
The expressions ~는 중이다/ ~고 있다 are normally translated to English with the use of "presently" or "currently".
This is my personal view. Any feedback is welcome.
I'd have thought regularly/habitually is more like 평소에. 항상 is, by the characters, "constant/regular(ly)". More constantly coming back to something as-a-rule than what we now think of as "regularly" though . . .
The equivalent of 진행형 ("(in-)progress(ive)" as in the progressive verb tenses, for "up-and-coming") really took off in Japan as a sort of slang recently, like in this BTS headline: https://news.joins.com/article/23161646 . . .
Thanks Sean. This is what I was trying to get feedback on:
(1) My hamster always sleeps => always: all the times; continuously non-stop; forever. [Adv of manner] = 제 햄스터가 항상 자요
(2) My hamster is always sleeping (/is sleeping as always/as usual) => always describes a regular event. [Adverb of frequency] = 제 햄스터가 언제나(처럼) 자요
What I am unclear is whether 항상 can be used in sentence (2), noting that there is a difference in the two English sentences. The continuous tense in sentence (2) is used to stress the negative aspect of the animal's sleep pattern.
Apologies for my rambling.