One of the most troublesome thing in making contract for mobile phone.
It is hard to find the shops which has staff who can speak your language.
(Japanese people are not really good at languages and so you sometimes feel inconvenient.)
There are 3 major mobile phone provider: au, docomo, Softbank.
Those companies provide information which shops you can find a staff who can serve you in your languges.
au
http://www.tvdenwa.com/list.html
(supporting by English, Chinese, Portuguese, Spanish, Korean, Vietnamese speaking staff through TV monitor)
docomo
https://www.nttdocomo.co.jp/english/support/shop/
(supporting by English, Chinese, Portuguese, Spanish speaking staff through TV monitor)
Softbank
http://www.softbank.jp/en/mobile/shop/
Basically, documents you need to submit for making contract are
If you want to pay monthly fee by credit card
- Passport(or Car license)
- Credit card
- Money for mobile phone itself
Paying by bank account
- Passport (or car license)
- Pass book of bank
- Money for mobile phone itself
If the address on your ID(passport and car license) is different, you need substitute document to certify that you are living in Japan such as, bill for gas, water, electricity, car license you got in Japan etc.