Add a configuration check for encoding detection

Author: Kevinjil

webapp/src/Service/CheckConfigService.php

@@ -189,6 +189,14 @@ public function checkPhpSettings(): ConfigCheckItem
                     (isset($sizes[$var]) ? Utils::printsize($sizes[$var]) : "unlimited"));
         }
 
+        $desc .= "\nFor submission encoding detection, the detect order should atcontain all expected submission encodings:\n";
+        $desc .= sprintf("  - `mbstring.detect_order` should at least contain `UTF-8` (now set to `%s`)\n", implode(', ', mb_detect_order()));
+        if (!in_array('UTF-8', mb_detect_order())) {
+            if ($result !== 'E') {
+                $result = 'W';
+            }
+        }
+
         $this->stopwatch->stop(__FUNCTION__);
         return new ConfigCheckItem(
             caption: 'PHP settings',

webapp/src/Utils/Utils.php

@@ -1069,7 +1069,7 @@ public static function reencodeUtf8(string $source): string {
                 return $encoded;
             }
         }
-        return "Could not display file as UTF-8, is it binary?";
+        return "Could not display file as UTF-8.\nCheck your PHP settings if you did not expect this file to be binary.";
     }
 
     /**