(99 Luftballons, which was mentioned here before, is arguably the bigger hit that really everyone knows. But I couldn't resist throwing this out there. It was a huge hit and is still known.)
Schrei nach Liebe by die Ärzte from 1993, German punk band. Everybody that ist Like 60 or younger knows that song. Well, maybe not if you're in your teens...
I have no idea how well known this is outside of Scotland, or at least the UK, but it meets all the other requirements: I'm Gonna Be by the Proclaimers, probably better known as 500 Miles
Portugal: Grândola, Vila Morena - Zeca Afonso. Probably not a hit when it came out, as it was banned by the dictatorial regime at the time but it became the anthem of our 1974 revolution, pretty much because it was the song that the revolutionary group chose to be played on the radio station (they took control of) to mobilize their forces.
Zeca Afonso has a bunch of other well-known (and really good) songs, all sung in Portuguese but this is the one most people know by heart. It helps that it gets played every year on the anniversary of the revolution and whenever there's a protest.
I dunno if this is legendary, but most people in Denmark know this song from school:
Livstræet (The (Norse) Tree of Life) from 1985: https://www.youtube.com/watch?v=hbSrdJF9hRg
The title of this song from 1974 became a German saying.
Udo Lindenberg, originally a jazz drummer, was the first German to make authentic German rock and pop music, in the German language, without it being "Schlager".
Alles klar auf der Andrea Doria (All clear on the Andrea Doria):
Oh, there are so many songs I could choose. Most hits from Brazil aren't well known outside. This one is a certified classic, though: https://www.youtube.com/watch?v=cOchidcyv9Q
There are so many good ones for Austria.
Probably have to go for Fürstenfeld by STS.
I have never met somebody in Austria who wasn't able to sing this, even (or especially) when drunk.