Symptoms
Receipts still use the US date format after I have changed my site to a different locale.
Cause
Dates/Times are stored in the database in the locale the DB is set to use. Even if the front-end is set to a new locale, if the DB is still on en-US, the receipts will be in US format.
Solution
In your notification.receipt.xml.config file, find this line:
<xsl:value-of select="OrderDate" />
...and change it to:
<xsl:value-of select="aspdnsf:FormatDate(OrderDate,'en-US','dd-MM-yyyy hh:mm:ss:tt')" />