I think I got a solution.
Just change the the 'donate' Button from your website from
<a id="donate" href="https://www.paypal.com/cgi-bin/webscr/?cmd=_s-xclick&hosted_button_id=TYJ2XQPG3SXPG" title="Make a donation">Donate</a>
to
<a id="donate" href="https://www.paypal.com/cgi-bin/webscr/?cmd=_s-xclick&hosted_button_id=TYJ2XQPG3SXPG&lc=US" title="Make a donation">Donate</a>
That worked for me :)