Here are a few options, depending on the context and formality:
Formal:
* Prynhawn da: This is the most literal translation and is appropriate for formal situations.
Informal:
* Prynhawn dda i chi: This is a more polite way to say "good afternoon" and translates to "good afternoon to you".
* Prynhawn da, sut mae'r pethau? This means "good afternoon, how are things?" and is a good way to start a conversation.
Other options:
* Prynhawn da iawn: This translates to "very good afternoon" and is a more emphatic way to greet someone.
* Bore da/Prynhawn da! If you are unsure of the time of day, you can say "good morning/good afternoon!".
It's important to remember that Welsh culture places a high value on politeness. Using a greeting like "Prynhawn da i chi" or "Prynhawn da, sut mae'r pethau?" is always a good choice.