chromium/third_party/blink/web_tests/accessibility/default-language.html

<!DOCTYPE html>
<html>
  <script src="../resources/testharness.js"></script>
  <script src="../resources/testharnessreport.js"></script>

  <body id="body" role="main">
    <p id="paragraph">Some text.
      <span id="span" lang="pl">Polish.</span>
    </p>

  <script>
    setup(() => {
      window.languages = internals.userPreferredLanguages();
      window.axRoot = accessibilityController.rootElement;
      window.axBody = accessibilityController.accessibleElementById('body');
      window.axParagraph = accessibilityController.accessibleElementById('paragraph');
      window.axSpan = accessibilityController.accessibleElementById('span');
    });

    async_test((t) => {
      assert_equals(window.axRoot.language, 'AXLanguage: en-US',
          'The browser language has not been changed yet.');
      assert_equals(window.axBody.language, 'AXLanguage: ',
          'The browser language should not inherit to body.');

      internals.setUserPreferredLanguages([ 'de' ]);
      t.step_timeout(() => {
        assert_equals(window.axRoot.language, 'AXLanguage: de',
            'The browser language has changed.');
        assert_equals(window.axBody.language, 'AXLanguage: ',
            'The browser language should not inherit to body after change.');
        assert_equals(window.axParagraph.language, 'AXLanguage: ',
            'The browser language should not inherit to paragraph after change.');
        assert_equals(window.axSpan.language, 'AXLanguage: pl',
            'The language of the span is controlled by the lang attribute.');

        internals.setUserPreferredLanguages(window.languages);
        t.done();
      }, 0);
    }, 'Tests if the browser language is correctly used to guess the language of the page.');
    </script>
  </body>
</html>