The configure-ecc skill (English source) and ja-JP top-level README plus
its configure-ecc translation documented `cp -r .../<lang>/* <target>/rules/`
for installing rule directories. rules/README.md explicitly warns against
this form because:
- Common and language-specific directories contain same-named files
(coding-style.md, testing.md, patterns.md, hooks.md, security.md).
Flattening makes each language overwrite the previous and common.
- The relative `../common/<file>.md` references in language rule files
break when common/ is no longer a sibling directory.
This is silent — the user gets only the last language's rules with no
error message.
Replace with the directory-form copy already documented in
rules/README.md:
cp -r .../<lang> <target>/rules/<lang>
Scope: English source + ja-JP. Closes#1879. Other locale translations
(zh-CN, ko-KR, pt-BR, tr) carry the same pattern and can follow up as
separate PRs to keep this change reviewable.