"I think that you are pretty."
Translation:Dw i'n meddwl fod ti'n bert.
Well as a fluent Welsh speaker, living in Wales and using the language every day, I would tend to at least make a nod to the presence of eich, with a 'ch at least. I would tend to drop the "dy" in "dy fod ti". But it is useful for a learner to learn it anyway, because without it, the mutation of bod=>fod would be difficult to understand.