English doesn't use the -ing suffix only for literally continuous actions. It's not equal to -taH.
In Lurveng's father is always complaining, you're not describing a continuous action, so -taH isn't appropriate. But reH can be used for things like habitual actions, as in this sentence.
beptaH lurveng vav means Lurveng's father continuously complains. He's not stopping. reH bep lurveng vav means Lurveng's father takes every opportunity to complain.
Why I asked about this is that every time I've tried to use an English -ing verb without -taH on the Klingon , it was marked wrong. So it seems like there are exceptions to this - using reH being one of the exceptions. Another seems to be when -mo' is used (e.g., I think the translation of "Qongmo' SoSwI', matamnIS" into "because my mother is sleeping, we need to be quiet" would be accepted). So I'm just trying to understand how/when -ing is allowed outside of the -taH suffix.
Unfortunately, the Duolingo course artificially requires -ing and -taH to mirror each other, even when inappropriate. And then they're inconsistent about it to boot, as this example shows. Unfortunately, you pretty much have to guess what the sentence writers are trying to get you to reply.
In reality, Lurveng's father always complains and Lurveng's father is always complaining are both perfectly valid translations of reH bep lurveng vav.
As an English speaker, I find it much more natural to say "I am running" than to say "I run", so I have been translating jIqet into the past or future tenses, because without any context - e.g., I run every Tuesday - or "I run whenever I can" - it's hard for me to imagine a situation where I would ever say only "I run". I'm using "jIqet" as an example here. It's the same with other formulations - jIQong, jISop. So seeing translations with -ing where there's no -taH to be seen has made me wonder about when -ing is allowed.
Forget the Duolingo course for a moment.
As you have noticed, English tends to use the present progressive instead of the simple present for actions that you're doing right now. When asked "What are you doing right now," you wouldn't answer "I run," you'd answer "I'm running."
In Klingon, the suffix -taH is not used for what English uses the present progressive. If someone asked you what you were doing, it would be perfectly find to answer jIqet. It means "in this moment, the action I am performing is 'run.'"
You could also answer jIqettaH, but this answer would mean "I am performing the action 'run,' and this action has been going on for a while and will continue to happen after this moment." It might be literally true, but if you're not talking about the fact that the running is an ongoing process, you don't need to say it. jIqet remains a perfectly valid response, and it's probably more likely, since you'd only add the -taH if you were building a context in which the continuousness of running were important.
Now back to the Duolingo course. They have decided that, in order to track whether a student recognizes the meaning of -taH, they're going to make -taH exactly equal to English present progressive. Anytime English says "I am running," the Klingons HAS to be jIqettaH. This is not correct, but they have decided to do this. It is, in my opinion, a poor choice, because it is teaching students a wrong meaning for -taH.
But, as you have seen, they are inconsistent with it. You can try to learn to plug the answer they want into the system, rather than the right answer, but you'll still come across examples like this that break their scheme.
Unfortunately, there's not much we can do about all this.
Klingon doesn't have a present progressive. It has a continuous aspect, which is similar to progressive tenses, but not identical.
Here's a good example. jun means evade. The Klingon Dictionary gives these examples:
yIjuntaH Take evasive action!
You can mirror this in the indicative mood:
jIjun I evade.
jIjuntaH I take evasive action.
Now, one would not normally say I evade; one would say I am evading. Even if it refers to a single swerve of the vehicle. Adding -taH, however, necessarily refers to more than one swerve; it's a series of swerves, and they've been going on before the current time and will continue to go on after the current time. It's "ongoing."
Klingon -taH and English -ing often DO overlap. But they're not identical.
The first two paragraphs are really helpful, thank you! I haven't come across this idea before of the present progressive in Klingon not being equal to that of English. Worf and other Klingons sometimes speak in English as if they were using the non-taH Klingon words, though. Sometimes when I'm translating a non-taH verb into the present tense, although I cannot imagine myself ever making such a statement, I can imagine them saying it. :D
I guess the course Moderators have to work within the limitations of Duolingo.