Translation to Japanese of learn-c.org

[osamu377]

Add Japanese Translation for Learn-C.org (C language)

Summary

This pull request adds a Japanese translation for Learn-C.org.

Motivation

• I am teaching C language at Technical School, and I need learning stuff.
• Japanese learners would benefit from having C language tutorials available in their native language.
• My goal is to help expand the accessibility of this great educational resource.

Changes

• Added Japanese translation files for the following sections:
  • tutorials/learn-c.org/jp (based on tutorials/learn-c.org/en)

Notes

• I tried to follow the existing formatting and style as closely as possible.
• Technical terms are kept consistent with standard Japanese C language textbooks.
• If any changes are desired regarding terminology or structure, I am happy to revise.

Request

Please review and let me know if:

• Any formatting adjustments are needed.
• Additional sections should be included in this PR.

Thank you for your time!