Root cause: no __init__.py in i18n/*/ subdirs, so setuptools
packages.find() skipped them. pyproject.toml also lacked
[tool.setuptools.package-data] for *.json glob.
Fixes:
- Add __init__.py to i18n/ and each language subdir (zh/en/jp/ko)
- Add [tool.setuptools.package-data] "*" = ["*.json"]
- Add build/ to .gitignore
Verified: wheel now includes all 4 i18n.json files.