no-duplicate-i18n-locales

Disallow duplicate entries in i18n.locales.

Targeted pattern scope

This rule targets docusaurus.config.* files and inspects i18n.locales when the locale array can be resolved statically.

What this rule reports

This rule reports duplicate locale values in i18n.locales, including duplicates introduced through identifier-backed arrays.

Why this rule exists

Duplicate locale entries add noise and can hide real i18n configuration mistakes during reviews. A deduplicated locale list is easier to maintain and reason about.

❌ Incorrect

export default {
    i18n: {
        defaultLocale: "en",
        locales: ["en", "fr", "en"],
    },
};

✅ Correct

export default {
    i18n: {
        defaultLocale: "en",
        locales: ["en", "fr"],
    },
};

Behavior and migration notes

This rule autofixes direct array literals by removing duplicate entries after the first occurrence.

When locales is identifier-backed, the rule reports and provides a suggestion that replaces the property value with an explicit deduplicated array literal.

When not to use it

Do not use this rule if your locale array is intentionally generated dynamically and duplicates are handled by external build-time tooling.

Rule catalog ID: R052

Further reading

• Docusaurus i18n guide