Issue #3035977: Rendered HTML Output doesnt respect activeLanguage completely

src/Language/StaticLanguageNegotiator.php

+<?php
+
+namespace Drupal\search_api\Language;
+
+use Drupal\language\LanguageNegotiator;
+
+/**
+ * Provides a language negotiator that allows setting the current language.
+ */
+class StaticLanguageNegotiator extends LanguageNegotiator {
+
+  /**
+   * The language code to return for all types.
+   *
+   * @var string|null
+   */
+  protected $languageCode;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function initializeType($type) {
+    $language = NULL;
+    $method_id = static::METHOD_ID;
+    $availableLanguages = $this->languageManager->getLanguages();
+
+    if ($this->languageCode && isset($availableLanguages[$this->languageCode])) {
+      $language = $availableLanguages[$this->languageCode];
+    }
+    else {
+      // If no other language was found use the default one.
+      $language = $this->languageManager->getDefaultLanguage();
+    }
+
+    return [$method_id => $language];
+  }
+
+  /**
+   * Sets the language code to return for all types.
+   *
+   * @param string|null $langcode
+   *   The language code to set.
+   *
+   * @return $this
+   */
+  public function setLanguageCode($langcode) {
+    $this->languageCode = $langcode;
+    return $this;
+  }
+
+}