WCAG 3.1.2 — Language of Parts

What this requires

The human language of each passage or phrase in the content can be programmatically determined, except for proper names, technical terms, words of indeterminate language, and words or phrases that have become part of the surrounding text's vernacular. In practice this means inline lang attributes on content that switches language.

How AI coding tools fail this

When generating multilingual content — a blog post quoting a French philosopher, a docs page with a German technical term, a product description listing a Japanese place name — AI tools render the foreign text without a lang wrapper. The page-level lang is set correctly (3.1.1); the inline switch is silent.

The second pattern: localised pages that mix locales. A Spanish marketing page that quotes an English testimonial without lang="en" on the quote. Screen readers force their default-locale phonics across both languages.

The third: code samples and product names treated as foreign language. They aren't — proper nouns and technical terms are an explicit exception.

Failing examples

A French phrase in English prose with no lang:

<p>
  The French expression "raison d'être" means "reason for being".
</p>

A multi-quote post mixing languages without markers:

<article>
  <blockquote>
    The unexamined life is not worth living.
    — Socrates
  </blockquote>
  <blockquote>
    Je pense, donc je suis.
    — Descartes
  </blockquote>
</article>

Passing examples

Mark the inline language switch:

<p>
  The French expression{" "}
  <span lang="fr">raison d'être</span> means "reason for being".
</p>

<article>
  <blockquote>
    The unexamined life is not worth living.
    — Socrates
  </blockquote>
  <blockquote lang="fr">
    Je pense, donc je suis.
    — Descartes
  </blockquote>
</article>

Edge cases

Proper names don't need lang. "París" in an English text is still pronounced as the user's screen reader pronounces "París" — marking it is unnecessary noise.
Borrowed words that have entered the language ("café", "résumé", "data") don't need lang.
Technical terms like CSS property names, code identifiers, and product names are exempt.
Region tags (lang="en-US", lang="pt-BR") help when pronunciation differs by region.
BCP 47 codes are the standard — two-letter ISO 639-1 with optional region.

How Jeikin handles this

The scanner can detect inline language switches via lexicon-based heuristics but the call is ultimately editorial. The dashboard surfaces suspected switches and lets the reviewer confirm or dismiss. The finding maps to WCAG 3.1.2.