1. Pick/choose a card, any card?
kaado o totte kudasai

2. Dont forget.
wasurenai de kudasai

3. Can i ask you to have dinner with me tonight? (politely)
isshoni bangohan o suru no wa dou deshou ka.

4. I am happy to see you again.
hard to translate. it would be more polite to say "thank you" for the last time you met. that would be "kono aida arigatou gozaimasu"

5. Are you Japanese? (politely)
"[person's name]-san wa nihon no kata desu ka?"

6. Its ok/ no problem. I understand.
hai, wakarimashita. "mondai ja arimasen yo " (no problem) or "ki ni shinai de kudasai." ("don't worry")

7. Dont worry.
ki ni shinai de kudasai.