"Oni pomagali policji."

Translation: They were helping the police.

[simiecia]

Why can't this be translated as "They helped the police"

[Jellei]

The perfective/imperfective (the one here) difference. In the original sentence, either they were helping the police regularly, or they were helping - and then we have no idea whether they managed to help or failed, maybe they weren't useful to the police in the end.

If they actually helped, succeeded in it, this would be "pomogli". And would denote a one-time help.

[JanKLinde]

I think I have to do it again... ;-)

"They were helping the police" doesn't say that they did it regularly. I highly recommend "They used to help the police".

[Jellei]

I agree with you in many examples, but I'm not sure if here. The first thing that comes to my mind is rather "I saw them somewhere doing something, I think they were helping the police with something". And then it's about the process, I don't know if they succesfully 'pomogli'. Sure, the 'regular' interpretation is possible as well (as I mentioned), but I think we both agree that it could use some more specific context.

[JanKLinde]

Yes, I didn't want to say that "they were helping" is generally wrong (only for "regularly"). Another possible context: "What were they doing when they were shot down?" – "They were helping the police."

[George829445]

Indeed, a mighty thin if any distinction in terms of practical interpretation for a native English speaker. Both versions clearly connote that help was provided in the past, and neither version really distinguishes between a longer or shorter duration, or whether or not it was a one time event or part if an ongoing process, etc..

[LucBE]

I disagree. This acronym (and possibly even more so your reaction) gave me an insight in contemporary Polish culture and street language, something I would not have gotten from the official Duo course.

[GP62HE]

Helping the police with their enquiries is the euphemism that the BBC often use, when someone actually has no choice

[Euhan1]

This sounds like a euphemism. "He was helping the police with their investigations when he suddenly bled to death..."

[BenYoung84]

How's that a euphemism?

[Diana76158]

we usually say "assisting the police with their enquiries" {assist/help)

[Jellei]

Sure, we can accept "assisting", added now.