It's the same tense, but a different aspect. Not every language has the luxury of being able to differentiate eg "I open" and "I am opening". These are called the perfective and imperfective aspects (not tenses or moods) respectively. I know that French doesn't (at least French verbs do not have formal aspects, but they can indicate them with tenses), Russian does (it actually uses a different form of the verb, sometimes very different, for the two aspects. I think that's the most difficult thing for foreigners to master), but not in the present tense, and it seems Arabic doesn't either.
No, I don't mean "more stringent and not flexible". I mean we're lucky to be able to express whether a present tense refers to continuous/habitual action - present simple, eg I open the window (eg every morning) - OR to immediately present/temporary action - I am opening the window (eg now) . I have greatly simplified the difference between the two aspects of the present. But the point is that the languages I know of, eg Arabic, French and Russian cannot do that simply by the form of the verb. They can of course convey the difference in meaning, but they have to use other means, such as adding an adverbial phrase of time.
Well done, KatieC, giving a primer on aspect. Greek has aspect, too. Distinctions between mood, tense, and aspect are very difficult nuts to crack for language learners. Deep dive with immersion is pretty much the only way to start to get a feel for the distinctions in a given language with aspect that is second nature to native speakers.
I don't think it's wrong so much as extremely weird. You could say "I am opening the window", which means "I am opening the window RIGHT NOW". If you say "I open the window", it would mean something like "I habitually open the window", or "I am the one who opens the window", or something like that.
You say, "why is the? needed above the definite article here?".
I can't see your symbol from my browser! Is the symbol over the ل? If it is, the لْ simply means the ل is in sukun. Originally, it is spelled as "l" but here the "لْ" is not pronounced because of the ش letter. So, it is 2ash-shubbaak (and not 2al-shubbaak).
Actually, putting the diacritics make Arabic easier to read. But, I guess sometimes many people get confused.
Update: Oh I can see it now, it is over the 2alif, اَ! No, it is just how the Duolingo writing style is. It is not a must, I assume they write it because they want to make sure that the original sound of the definite article is "2al".
"2ash-shubbaak" -> "2aftaHu 2ash-shubbaak" or "2aftaHush-shubbaak".
The word الشباك, even though we don't give any diacritic marks (whether there is a little thing on top of alif or not), is always pronounced as "2ash-shubbaak. So, it is:
-- (1) "2aftaHush-shubbaak(a)" or "2aftaHu 2ash-shubbaak(a)" if we follow Formal Standard,
-- (2) "2aftaH 2ashubbaak" if we say it in inFormal Standard
-- (3) "2aftaHish-shubbaak" if we use Duolingo's style.
The diacritic marks are optional, are a tool to help the beginners who cannot read Arabic perfectly. (If you have heard something else, perhaps, there is an audio glitch).
(1) "is it easier for other people to hear between "a window" and "the window" here?"
It is "a window" = shubbaak شبّاك and is "the window" = 2ash-shubbaak الشّباك. So, there is the double "sh" sound at "the window". But, if we pronounce the words in the formal standard, actually it will be clearer, ie. "a window" = shubbaak(un) شباكٌ and the window = "2ash-shubbaak(u)" الشباكُ . There is "-un" in "a window" and "-u" in "the window". -- The audio that we hear is something done by some advanced conversationalists who neglect almost all the ending sounds (and Standard). So, indeed, it is hard a bit.
(2) "would it be more of a clear-from-context thing?"
Yes, it would be.