How would you do it without Wikis? Is there a book somewhere in game that has the translation?

There may have been such a book in Oblivion, where they played a much bigger part. They certainly didn't waste the time spent writing the books in Morrowind, and then Oblivion since most of the ones you find are reruns. It's possible that book is here, somewhere, but you'd have better luck using the wiki for Oblivion.

I don't know about Daggerfall or Arena, but Morrowind had the stone of Rosetta with the signs near the towns. As soon as you notice that they look different in each town, you'll start to assume that they aren't just random gibberish or random pieces of art. Then you need to assume that they say the same as the name of the town which you already know. And then you end up in a while with the alphabet.

If you look at the GOTY map for morrowind (should be on google images if you don't have it) you will see vvardenfell, solstheim and mournhold have daedreic writing above their names, translate them, most daedric letters seem to look like normal letters, I managed eventually

I think the conclusion here is that a few words are guessable, and then the rest is figured out. Even with having some spoiler knowledge (which I tried not to use), I still had trouble with the