What's wrong
Values like `lang="english"` or malformed region codes cause speech synthesis software to fail.
Who it affects
Screen readers fall back to default speech synthesizers or report language parsing errors.
How to fix on WordPress
Use WordPress's native `language_attributes()` function which extracts valid codes configured in General Settings.
Code example
Problematic Code
PHP
<html lang="en_US_custom">Recommended Accessible Code
PHP
<html <?php language_attributes(); ?>>How to check your fix
Validate the `lang` tag against the IANA language subtag registry (e.g. `en`, `en-US`, `fr`, `de`).