I do not agree with you. If I learn French, there is an automatic French context to the language acquisition. Likewise with Irish and with all other languages.
Also, it's only one sentence not a paragraph or essay, which may well have different contexts. One sentence at beginners stage is normally within the context of the language that is being studied.
I don’t think you’ve considered that it could be in a Northern Ireland rather than an Republic of Ireland context, both of which be could be discussed in an Irish context. There are different police forces for both jurisdictions. The word choice in the original sentence would strongly suggest the latter, but it could equally refer to any police force around the world.
If a person is not Irish and learning here, they are less likely to offer “guards/Gardaí” as a translation of “póilíní”, as that would require them to know another Irish word and that it is used to refer to the police force in the 26 counties.
If anyone should wish to know more details about Irish society and culture, beyond the language, I think that is largely outside of the remit of a course of this nature, although I would encourage them to read the relevant Wikipedia entries for a broad overview of the relevant history of policing in all parts of Ireland in the last century.
I'm English, and I was initially very confused, because I have always thought that the term for police in Irish is "gardai". Having read through the discussion here, I understand why the generic term has been used in these lessons, but I would have really appreciated a note explaining this when the term was translated.
For a moment, I wondered whether I'd accidentally swapped language courses. Mind you, it is quite early in the morning, and I'm easily confused... :-)!
Just wanted to say that I live in Canada near the "Gaeltacht Bhuan Mheiriceá Thuaidh" and the Irish speakers I know from this area and from America would also use póilíní and not Garda or Gardaí so it makes sense to me to learn póilíní with this course! Thought I'd let you know, since you seem to be getting a lot of backlash for it.