You technically may be right, perhaps a better interpunction in Polish would be a semicolon (or dividing it into two sentences), but frankly... I don't think that almost anyone cares about that in Polish. It seems perfectly natural to me to use a comma here in Polish.
And from what I understand, in English most people also wouldn't notice a problem. Anyway, using such a different interpunction in the English sentence, even if it was better, would be rather confusing.
Commas splices are okay in informal English, but only when their meaning is clear. The meaning isn't clear here because the sentences have two different functions (imperative v. statement) and two different subjects, the latter of which has no pronoun. A comma splice like, "This man is suffering, you must help him," is still technically incorrect, but understandable because the change of subject is cued by the 'you'. "This man is suffering, help him," doesn't cue the change of subject, and simply isn't readily understandable. I have to break it down to figure out what meaning is intended by it, and work around the mistakes of the person who wrote it, which is not ideal when you're learning a new language.
The sentence should be changed to something else that makes sense in both English and Polish. You think an English speaker might not notice, but I think any native English speaker will be confused by this statement. It reads like Engrish.
As a native speaker, it makes sense to me at first glance without stopping to think... It just looks like normal informal English to me, though of course not technically correct.
The problem is, a comma is the natural punctuation in Polish, and if the English is changed then the two are completely different. And as this course is teaching Polish, natural Polish is more important than natural English when you can't have both. In fact, the English being unnatural for you might help you remember what's natural in Polish.
Obviously a comma splice in the English isn't perfect, but sometimes we just can't have both perfect Polish and perfect English without them being too different, and in those cases it has to be the English that suffers.
No language translates perfectly to another language. That isn't the issue. Whoever wrote this bit of the course picked this sentence to illustrate a particular grammatical point, and this sentence is awkward as hell and a bad example. Whatever grammatical point this sentence is meant to be showing, it can and should be shown with a different, better sentence.
Not to mention, it is totally fair to expect a change from comma to period if the language punctuation conventions are that diverse between the two languages.
From my UK perspective, suffering is an umbrella term covering various kinds of pain (alik's comment hints that cierpieć works similarly):
- hurt: e.g. his leg is broken / he has an open wound
- severe physical discomfort: e.g. he is homeless, it's freezing, and he has no warm coat.
- emotional pain: e.g. his entire family recently died in a car crash
- mental pain: e.g. he is suffering from untreated clinical depression. [5 Nov 2019 12:13 UTC]