Add Japanese (ja-JP) locale support

[heyjosephme]

Checklist

• I have read and accepted the contributing guidelines.

Is your feature request related to a problem? Please describe

The jekyll-theme-chirpy theme currently lacks Japanese (ja) locale support, which means Japanese users cannot have a fully localized blog experience. This affects UI elements, date formats, and navigation labels that should be properly displayed in Japanese for better user experience and accessibility for Japanese-speaking users.

Describe the solution you'd like

I propose adding Japanese locale support by:

Creating a new locale file ja-JP.yml in the _data/locales/ directory
Adding translations for all existing UI strings and labels in Japanese
Implementing proper date formatting for Japanese date conventions
Ensuring proper font support and text rendering for Japanese characters

Describe alternatives you've considered

No response

Additional context

No response

[cotes2020]

Hi there! Thank you for your suggestion. As you can see, most of the locale translations in this repository are contributed by enthusiastic developers from various countries in the community. So if you are proficient in Japanese, you are welcome to submit a PR.