docs: fix translated README links

[coyaSONG]

Summary

Fix stale relative link targets in the Russian, Korean, Japanese, and Chinese READMEs under doc/.

The paths now resolve from each translated README's actual directory to:

• the current Manpage syntax at assets/syntaxes/02_Extra/Manpage.sublime-syntax
• the local assets.md and alternatives.md pages
• the repository-root contribution guide and license files

Only link destinations changed; translated text is untouched.

Validation

• resolved every relative Markdown link in the four translated READMEs against its source-file directory: zero missing targets
• resolved every relative HTML href in the same files: zero missing targets
• verified the Manpage syntax path from the current repository tree
• git diff --check

No changelog entry is included because CONTRIBUTING.md exempts documentation and typo fixes.

Closes #3839