"Dyw e ddim yn dalentog."
Translation:He is not talented.
Because that's not how you form the negative of mae in Welsh :)
(You might as well ask why we say "I didn't go" instead of "I went not" in English -- that's just not how you form the negative of "go".)
Mae ... turns into dydy ... ddim or dyw ... ddim depending on dialect.
With dw, you don't see the difference in the everyday short forms (dw i versus dw i ddim), but in the longer forms used in some textbooks you'll see a difference between positive rydw i and negative dydw i ddim, where the negative has the same d- in front as dydy.
Thank you for such a detailed response! I only started learning Welsh a few weeks ago so I'm still getting the hang of the basics. :)