So every artistic tool, every trope, every use of figurative language, every symbol is ironic.
Or it's just a shitty "definition" and you're high.

LOL IRONIC FINGER QUOTES!!1!

Okay? In my world view, sarcasm naturally depends on irony. Just for fun and giggles, can anyone say something sarcastic which doesn't use irony?

Ironically stupid.

Don't know about Danish but I guess language barriers may be at work here. Germans and Poles obviously do know the word "sarcasm" but in many cases where "sarcasm" is used in English, it's "irony" in German or Polish (especially in German, as far as I can tell). Guess the connotations differ notably throughout languages.

What (in turn) is then used for irony in German or Polish?

Dunno about the whole irony thing, but I think some developers use the older game styles simply because it allows them to turn their game concept into reality without requiring big-budget resources. In those cases, the style is almost a necessity and there isn't anything ironic about that.

In order to have an expression of irony, there needs to be some kind of juxtaposition between the fact that the game is new, but styled like an old one.

Primordia is simply a new adventure game that evokes the look, gameplay and general feel of one made in the mid-90s, with a moody atmosphere and a serious, sincere story.
There is no irony here. The game's overall effect would be no different if it actually had been released in 1995.

For an ironic (at least in the hipster sense) usage of pixel-art retro graphics, look no further than Fez. This is a game that deliberatly looks kind of like a platformer on a system like the SNES, but it uses a central game mechanic that would have been largely impossible to do on that sort of hardware, is infused with modern pop culture references and even has gimmicky stuff like that puzzle consisting of a QR-code, all of which draws constant attention to the fact that it is, in fact, a new game.

Retro City Rampage also fits into this. A game with the basic structure and gameplay of GTA 3, but with graphics, characters, themes and various mechanics based on NES-era titles. Add to this the numerous references to and parodies of both old and recent pop culture, and you do have an overt case of irony.

You mean that shitty film where characters constantly go "Hey, look at us! Our situation is totally following the rules of a slasher movie!" Yeah, really subtle.

Irony talks about a situation that part of the audience knows more about (Yeah, your car's paint is just fine), while sarcasm is a mean comment towards a person (You are such a good driver).

That might be true for some specific titles that consciously poke fun at 80's or 90's gaming, but it certainly doesn't apply to all low-res/retro-style games. Like Judas said, the developers of Primordia wouldn't consider their game, graphics or mechanics outdated, and they didn't make the game that way as a joke.

Well, irony. My impression is that the threshold at which something is referred to as sarcasm is simply higher in German and Polish than in English.

That definition is far too general to be of any use though.

Technically, any game with a meaning beyond what it it presents point blank is ironic by that definition.

This means that SpecOps: The Line, Prince of Persia: The Two Thrones, and even something like Far Cry 3 are all ironic games because they deal with meanings beyond what they present (Horrors of war, growing up and accepting responsibility for mistakes and destiny versus free will, respectively) . And none of those games are "retro".

I think it is more correct to say that the retro style is an aesthetic choice than an attempt to be ironic. When a developer makes a game, they have in their mind an art style they think is appropriate, and sometimes the 8 bit art fits the design they want better

Perhaps, but I still say Freud was a total closet case.
Or the long answer: NOOOOooooo. :-P

No, they aren't the same thing. So its more than just a linguistic barrier we're seeing at play here.
that would make it a satire, spoof or parody. Not neccesarily ironic.

No....

https://www.youtube.com/watch?v=awD1gtpdWIA