Check ja (日本人) locale and fix typos

Check locales by native and fix typos.

Project use [jekyll-multiple-languages-plugin](https://github.com/kurtsson/jekyll-multiple-languages-plugin). Each locale file are keeped in `_18n` folder.
For example `en` is located in `_18n/en.yml` file.

Project was translated by translation service not by human. So it can keep typos.

Need to check current issue language.

- Fork
- Create branch 178_ja_locale
- Commit and create PR

Inspect the Japanese locale in _18n/ja.yml, using _18n/en.yml as a reference for the locale layout. Review the Japanese text for typos and commit the corrections on the requested branch; done means the ja locale contains corrected wording and a pull request is opened.

Written by the indexing model from the issue text.