# `react-doctor/lang` Use a valid BCP-47 language tag on `` (e.g. `en` / `en-US`). - **Category:** Accessibility - **Severity:** warn - **Source:** oxlint-plugin-react-doctor - **Framework:** global - **Enabled when:** always - **Documentation:** ## Validation prompt Use this to decide whether a fired diagnostic is real or a false positive. Fires on a `` element (including `` or a component resolved to "html" via jsx-a11y polymorphic/components settings) whose `lang` prop is invalid: explicitly `lang={undefined}` or `lang={null}`, or a static string whose value fails BCP-47 validation — the primary subtag must match a known ISO-639 tag and every `-`/`_`-separated subtag must be alphanumeric. A dynamic value like `lang={foo}` is NOT flagged. False positive: the primary-tag set is a partial, hand-maintained ISO-639 list, so a genuinely valid but uncommon or newer language tag absent from that set is wrongly reported. ## Fix prompt Use this once validation confirms the diagnostic is real. Set `lang` to a valid BCP-47 / IANA language tag — `` or a region-qualified ``, script-qualified `` as needed. Never leave it as `lang={undefined}` or `lang={null}`; if the value is computed, ensure it always resolves to a real tag. If the linter rejects a tag you've confirmed is valid (e.g. a rare ISO-639 code), it's a known gap in the rule's partial tag list — suppress that line with a justifying comment. See https://oxc.rs/docs/guide/usage/linter/rules/jsx_a11y/lang