Formal:
* 遊びましょう (Asobimashou): This is the most formal way to say "let's play" and is suitable for situations where you are talking to someone older or in a formal setting.
* 一緒に遊びましょう (Issho ni asobimashou): This means "Let's play together" and is also quite formal.
Informal:
* 遊ぼう (Asobou): This is the most common and informal way to say "let's play."
* 一緒に遊ぼう (Issho ni asobou): This means "Let's play together" and is informal.
More specific:
* ゲームをしよう (Gēmu o shiyou): "Let's play a game."
* サッカーをしよう (Sakkā o shiyou): "Let's play soccer."
The best translation will depend on the situation and your relationship with the person you are talking to.