added Utils method to get device language

deltachat-ios/Helper/Utils.swift

@@ -161,6 +161,14 @@ struct Utils {
             return nil
         }
     }
+
+    static func getDeviceLanguage() -> String? {
+        // some device languages have suffixes (like en-aus etc.) so we want to cut suffixes off
+        guard let lang = Locale.preferredLanguages.first?.split(separator: "-").first else {
+            return nil
+        }
+        return String(lang)
+    }
 }
 
 class DateUtils {