"I watched the TV on Thursday."
Translation:Edrychais i ar y teledu ddydd Iau.
aren't you supposed to say "gwyliais i'r teledu" instead of "gwyliais y teledu"? I thought you were supposed to add -ais i to the verb stem?
gwyliais i'r teledu is the usual colloquial form for 'I watched television'.
(Dropping the pronoun i is normal in the formal register of the language, but it is probably best to keep things simple and avoid the formal register for now.)