Not really. The relativists aren't saying "oh, your 4 translates to their 5", and in fact are trying to say that such a statement is impossible to make. Your attempt at translation assumes the existence of some culture-independent thing, and tries to say "4" and "5" are different culture-specific symbols for representing that culture-independent thing, whatever it may be. The relativist position is that no such culture-independent thing exists.

In other words, the relativist believes that:

* If a culture decides this many objects (represented by dots): ". ." combined with this many other objects: ". .", produce this many objects: ". . . . ."

* Then that decision is just as valid and just as true as our culture's decision that ". ." objects and ". ." objects make ". . . ." objects.

The fact that every culture we know of has adopted the second one instead of the first is then explained as some sort of massive coincidence, or perhaps the result of some very old "2 + 2 = 4" culture successfully imposing its norms on everyone else such that it has persisted as a cultural belief to the present day.