How to fix valid lang on BigCommerce

Steps for BigCommerce

1. Go to Storefront → My Themes → click Customize on your active theme, then Advanced → Edit Theme Files.
2. Open templates/layout/base.html (or the equivalent layout file for your theme, e.g. Cornerstone uses templates/layout/base.html).
3. Find the <html> tag and set it to <html lang="{{locale_name}}"> — BigCommerce's Handlebars context exposes locale_name as a valid BCP 47 code.
4. Click Save & Apply.
5. For inline foreign-language text in product descriptions, use the HTML source editor in the product description field (Products → Edit Product → Description → click the <> HTML button) and add a lang attribute to the relevant tag.

What is valid lang?

Every HTML page has a primary language declared on its `<html>` tag (e.g. `lang="en"` for English). When a block of text on that page is written in a different language — a French product description on an English store, for example — that element needs its own `lang` attribute with a valid language code so assistive technology knows to switch pronunciation rules. The "valid-lang" rule fires when a `lang` attribute exists on an element but contains an unrecognised or misspelled value (e.g. `lang="english"` instead of `lang="en"`, or `lang="en_US"` instead of `lang="en-US"`). Valid codes follow the BCP 47 standard: a two- or three-letter primary subtag (`en`, `fr`, `de`, `zh`) optionally followed by a region subtag after a hyphen (`en-US`, `fr-CA`, `zh-Hant`).

Screen readers such as JAWS, NVDA, and VoiceOver use the `lang` attribute to select the correct text-to-speech voice and pronunciation engine. An invalid value means the reader either ignores the instruction or speaks the text with completely wrong phonetics, making your content incomprehensible to blind and low-vision shoppers. WCAG 2.1 Success Criterion 3.1.2 is a Level AA requirement, meaning failure can expose your store to accessibility lawsuits (ADA, Section 508, EU Accessibility Act). Beyond legal risk, Google uses language signals to serve your pages to the right regional audiences — incorrect or absent language markup can suppress your rankings in multilingual search results and reduce qualified organic traffic.

See the complete Valid lang guide for every platform and the full background.