"Dewi Lingo is the wettest."
Translation:Dewi Lingo yw'r gwlypa.
Yes. You need an emphatic sentence with a superlative, and that (yw in this case) goes in the middle. You do not use an extra verb at the beginning as well.
I think that historically there would have been a verb at the beginning, as that is the basic word order in Welsh, but it would have been a different verb, and I don't even know if anyone knows what it was.