Bug#1039587: stopwatch: Add Japanese language support

[Green <usergreen@users.osdn.me>]

Package: stopwatch
Version: 3.5-6
Severity: normal

Dear Maintainer,

I have translated this application into Japanese.
Please add Japanese version in the next release for the convenience of users in Japanese.

Best regards,
Green

-- System Information:
Debian Release: 10.13
  APT prefers oldoldstable-updates
  APT policy: (500, 'oldoldstable-updates'), (500, 'oldoldstable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.19.0-24-amd64 (SMP w/2 CPU cores)
Locale: LANG=ja_JP.UTF-8, LC_CTYPE=ja_JP.UTF-8 (charmap=UTF-8), LANGUAGE=ja_JP.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages stopwatch depends on:
ii  tk  8.6.9+1

stopwatch recommends no packages.

stopwatch suggests no packages.

-- no debconf information