Language:
Japanese is the official language, but don't worry, in big cities like Tokyo and Osaka English is quite common, especially in tourist places. 

Currency:
The currency is the Japanese Yen (JPY). You'll quickly get used to doing mental calculations while figuring out how much those irresistible purchases or onigiris from the supermarket cost.

Credit cards and ATMs:
In larger cities you can pay for almost everything with a card, but don't be overconfident. Local markets, temple entrances or the most authentic corners are usually "cash only". If you need cash, 7-Eleven ATMs or post offices are your best friend, they accept international cards without any problems.

Plugs:
Here, A and B type plugs are used, with a voltage of 100 V. My recommendation? Take a universal adapter with surge protection and, if you carry tools such as hairdryers or straighteners, a voltage converter to avoid surprises.

Security:

Japan is among the safest countries in the world. However, as with any other place, do not forget to use common sense.