"We eat dinner."
Translation:Vi äter middag.
"Middag" used to be the meal you had at midday (and still is in some areas away from Stockholm) and in the evening you had "kvällsmat" or "kvällsvard". I think it changed when they removed Saturday school, so that you only had 5 school days per week (and so the newly borrowed English word lunch fit with on letter for each day on the school schedules instead of the six-letter middag which was used for the schedules with sixs days) back in the 50s. I still use "middag" as the meal at midday.
I agree with you - "Vi äter kvällsmat" ought to be a valid translation, as "kvällsmat" is what I (as a Swede) eat in the evening (and I use it even if I have a three dish meal in the evening). I eat "middag" at noon, and I never eat "lunch". Some Swedes eat "lunch" at noon and "middag" in the evening (which I always find completely absurd, but I know the concept exists), so both "middag" and "kvällsmat" ought to be accepted translations of "dinner".
Indeed, and "kvällsmat" ought to be accepted as translation of "dinner" as some Swedes (myself included) use "kvällsmat" for the big meal eaten in the evening (and "middag" for the meal eaten at noon). Some Swedes use "lunch" for what they eat at noon and "middag" for the meal they have in the evening (absurd concept from my point of view, but definitely used), which is probably the reason why they have "middag" as the translation of "dinner" here.
Sometimes people ask me "Ska vi äta middag nu?" ("Are we going to have dinner now?") and I answer "Nej, det åt jag för sex timmar sen." ("No, I had that six hours ago."). Those people usually give me a scowl and add "Äh, skärp dig - du vet vad vi menar!" (Oh, come on - you know what we meant!), and all this confusion because some people moved "middag" to the evening... :-)