The {invoice_date} is not working. On every invoice it shows 10 October 2012.
And it is showing in English but my site is in Dutch.

Hello,

you can set date format in General config. If you need month in text form and dutch language, it is not possible at the moment. If you need it immediately, you could do it this way:

Open administrator/components/com_vminvoice/helpers/invoicehtml.php and modify all rows, where is $dateStr.
For example:
$replacement = gmdate($dateStr, $shippingDate);

will be modified to:
$replacement = gmdate('j', $shippingDate).' '.JText::_(gmdate('F', $shippingDate)).' '.gmdate('Y', $shippingDate);

JText on month should translate it to dutch language if you have dutch as a main language.

Modify only for invoice_date:
Your invoice_date is around row 424 and will be look similar:
$replacement = gmdate($dateStr,$invoiceDate);
change to:
$replacement = gmdate('j',$invoiceDate).' '.ucfirst(JText::_(gmdate('F',$invoiceDate))).' '.gmdate('Y',$invoiceDate);

It worked. Thanks!