Merge pull request #15 from l/translation_ja

Update Japanese translations
Fix typo in a news
Use https for WeeChat URL in README
Use https for links to github.com
Use longer key ID in gpg commands
Add more detailed instructions for Debian packages below the repositories
Add "aptitude update" in instructions for Debian repositories
update German translations
Use command "sudo" in instructions for Debian repositories
update German translations
Update Japanese translations