"Cia mheud càr?"
Translation:How many cars?
This is easier to explain in the UK that the US.
There historically was a tendency in European languages not to pluralise weights and measures. In the UK it is equally common to say £2.50 with the £ in singular (two pound fifty) as it is in plural (two pounds fifty). This tendency can still be heard in weights in old-school markets -- "two pound for three fifty" (i.e. 2lb for £3.50) and the like, although the move to metric helped move this old pattern closer to the grave. People who still weigh themselves in stone still do exactly that -- weigh themselves in "stone" -- but in metric everyone pluralises. When I describe my weight it's either "stone" or "kilograms".
This pattern exists in Gaelic too, but how well it's adhered to differs from person to person, and pluralisation is getting more common due to the influence from English.
How does "cia mheud" come into this? "meud" means "measure, quantity", so the weights-and-measures rule applies.
Can I jump in here to say that I've just reached this point today, and I've exclusively had "cò mheud" in the questions and never "cia mheud", but from the forum it sounds like others have had "cia" questions? I've been googling it because I've never heard it before and "cia mheud" is what's in the GOC. Has something changed the questions to say cò now, if cò was only an accepted translation before?
There's a nuace here. You wouldn't say "how many car?" in English because it'd be wrong. So even though the question translates to that, we infer the meaning as "cars" since cia/cò mheud takes the singular. Remember you never translate directly from one language into another.