Add regression test for #11870

Closes phpstan/phpstan#11870

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

tests/PHPStan/Analyser/nsrt/bug-11870.php

@@ -0,0 +1,14 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11870;
+
+use function PHPStan\Testing\assertType;
+
+function () {
+	assert(isset($v) && is_array($v) && isset($v['LANGUAGE']));
+
+	$language = $v['LANGUAGE'] !== 1 ? 'en' : '';
+	if ($language !== '') {
+		assertType('true', $v['LANGUAGE'] !== 1);
+	}
+};