With 1+1=2 as an example I would like to apply a quick real world application.
1+1=2 is simply the concept that you have one of one thing and one of another, so we call that two.
So in essence you have:

this apple. Then someone gives you another apple, now you have two:

So if an alien were to see this process he would have different words for it, or a different way of describing the concept, but they would definitely agree that there is a concept in which you name an amount of one thing or another.