Feature main 7512 use accept language (#10611)

* #7512 Added Accept-Language header into the locale detection

* #7512 Fixed call to PKPRequest::getPreferredLanguage()

* #7512 Give preference to the server preferred locale if there's no match with the Accept-Language header

* #7512 Updated code to use the Laravel request directly

Author: jonasraoni

classes/core/PKPRequest.php

@@ -65,7 +65,6 @@ class PKPRequest
     /** @var string user agent */
     public string $_userAgent;
 
-
     /**
      * get the router instance
      */
@@ -593,7 +592,7 @@ public function getUserVar(string $key): mixed
     {
         // special treatment for APIRouter. APIHandler gets to fetch parameter first
         $router = $this->getRouter();
-        
+
         if ($router instanceof \PKP\core\APIRouter && (!is_null($handler = $router->getHandler()))) {
             $handler = $router->getHandler(); /** @var \PKP\handler\APIHandler $handler */
             $value = $handler->getApiController()->getParameter($key);

classes/i18n/Locale.php

@@ -134,7 +134,8 @@ public function getLocale(): string
         $request = $this->_getRequest();
         $locale = $request->getUserVar('setLocale')
             ?: $request->getSession()->get('currentLocale')
-            ?: $request->getCookieVar('currentLocale');
+            ?: $request->getCookieVar('currentLocale')
+            ?: $this->getPreferredLocale();
         $this->setLocale($locale);
         return $this->locale;
     }
@@ -582,4 +583,19 @@ private function _getSubmissionLocaleNames(): array
                 ->toArray());
         })();
     }
+
+    /**
+     * Retrieve the preferred user locale from our supported locales using the Accept-Language header
+     * If there's no match, it falls back to the server's primary locale
+     */
+    private function getPreferredLocale(): ?string
+    {
+        $serverPreference = $this->getPrimaryLocale() ?: LocaleInterface::DEFAULT_LOCALE;
+        $supportedLocales = array_values($this->_getSupportedLocales());
+        // Move the server preference to the top, in case the user preference doesn't match with the supported locales, the server one will be picked
+        if (is_int($index = array_search($serverPreference, $supportedLocales))) {
+            array_splice($supportedLocales, $index, 1);
+        }
+        return app(\Illuminate\Http\Request::class)->getPreferredLanguage([$serverPreference, ...$supportedLocales]);
+    }
 }