"I believe I am right."
Translation:Dw i'n credu mod i'n iawn.
Which seems a bit confusing doesn't it.
However it is only 'very' with a noun, eg da iawn; mawr iawn etc
On its own it conveys a general positivity, which can be translated into numerous words in English depending on the context.
Sut dych chi? Iawn diolch - How are you? Fine thanks.
Atebais i'r cwestiwn yn iawn - I answered the question ok.
Sut aeth y daith? Yn iawn, diolch - How did the journey go? Well thanks.
(Note in the first example there should be a 'yn' before the iawn but it gets dropped in speech)