chromium/third_party/blink/web_tests/svg/dom/systemLanguage-case-insensitive.html

<!DOCTYPE HTML>
<title>The "systemLanguage" attribute matching is case insensitive (eg. "en" matches "EN")</title>
<link rel="help" href="https://www.w3.org/TR/SVG2/struct.html#ConditionalProcessingSystemLanguageAttribute">
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<svg id="mysvg">
</svg>
<script>

async function languageChange() {
	return new Promise(resolve => window.onlanguagechange = resolve);
}

promise_test(async () => {

	var languageChangePromise = languageChange();
	testRunner.setAcceptLanguages("en");
	await languageChangePromise;
	var text1 = document.createElementNS('http://www.w3.org/2000/svg', 'text');
	text1.setAttribute('systemLanguage', 'en');
	text1.textContent = 'English-US';

	var mysvg = document.getElementById("mysvg");
	mysvg.appendChild(text1);

	assert_greater_than(text1.getBoundingClientRect().width, 0);

	mysvg.removeChild(text1);

	text1.setAttribute('systemLanguage', 'EN');

	mysvg.appendChild(text1);

	assert_greater_than(text1.getBoundingClientRect().width, 0);

});

</script>