special characters in email from iOS app - localizable

hello, I use localizable to add German language to my app, that works. However when I add special characters like ü, then they are not shown but special signs appear like: für

How can I make the real characters appear like ü.

This I have for example in localizable German:
"Bedankt voor je bestelling bij Schiffer Food Trading.\n<br><br>" = "Vielen Dank für Ihre Bestellung bei Schiffer Food Trading";