Formal:
* ยินดีที่ได้รู้จัก (yin di thi dai roo chak): This is the most formal and polite way to say it, literally meaning "I am happy to have known you."
* ยินดีที่ได้พบ (yin di thi dai pob): This is also formal and translates to "I am happy to meet you."
Informal:
* ดีใจที่ได้รู้จัก (dee jai thi dai roo chak): This is a more casual and friendly way to say it, meaning "I am happy to have known you."
* ดีใจที่ได้เจอ (dee jai thi dai jer): This is also informal and translates to "I am happy to meet you."
For a new acquaintance:
* ยินดีที่ได้รู้จัก (yin di thi dai roo chak): This is the most common way to say it when meeting someone for the first time.
For someone you already know but haven't seen in a while:
* ดีใจที่ได้เจออีก (dee jai thi dai jer ik): This translates to "I am happy to see you again."
You can also add "khrap" (for men) or "kha" (for women) at the end of any of these phrases to show extra politeness.
Here are some examples:
* ยินดีที่ได้รู้จักครับ (yin di thi dai roo chak khrap): (Formal, to a man)
* ดีใจที่ได้เจอค่ะ (dee jai thi dai jer kha): (Informal, to a woman)
* ดีใจที่ได้เจออีกนะ (dee jai thi dai jer ik na): (Informal, to a friend)
Remember that the best way to say "nice to meet you" in Thai depends on the situation and the person you are talking to.