oxc-project/oxc · error

`lang` attribute must have a valid value.

Error message

`lang` attribute must have a valid value.

What it means

Raised by jsx-a11y/lang when the lang attribute value on an element is not a valid language tag according to the language-tags (BCP-47) parser. Invalid tags prevent assistive technology from determining the content language.

Source

Thrown at crates/oxc_linter/src/rules/jsx_a11y/lang.rs:18

use language_tags::LanguageTag;
use oxc_ast::{
    AstKind,
    ast::{JSXAttributeItem, JSXAttributeValue},
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::{GetSpan, Span};

use crate::{
    AstNode,
    context::LintContext,
    rule::Rule,
    utils::{get_element_type, get_prop_value, has_jsx_prop_ignore_case},
};

fn lang_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("`lang` attribute must have a valid value.")
        .with_help("Set a valid value for `lang` attribute.")
        .with_label(span)
}

#[derive(Debug, Default, Clone)]
pub struct Lang;

declare_oxc_lint!(
    /// ### What it does
    ///
    /// The lang prop on the `<html>` element must be a valid IETF BCP 47 language tag.
    ///
    /// ### Why is this bad?
    ///
    /// If the language of a webpage is not specified as valid,
    /// the screen reader assumes the default language set by the user.
    /// Language settings become an issue for users who speak multiple languages
    /// and access website in more than one language.

View on GitHub (pinned to e1e7af627c)

Solutions

  1. Use a valid BCP-47 language tag such as "en", "fr", or "zh-Hans".
  2. Check for typos, stray whitespace, or empty strings in the lang value.
Defensive patterns

Strategy: validation

When it happens

Trigger: Thrown at crates/oxc_linter/src/rules/jsx_a11y/lang.rs:18 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/4412af1f2446482f. Report an issue: GitHub.