This is one article in the larger Troubleshooting SharePoint Alerts guide

Problem

The date format in emails received from workflow notification emails such as Task Assigned do not use the correct (site) date format.

For example you may get emails with US date formats for a site using UK date formats and vice versa.

References

• Date Format Incorrect in Email Task Alerts
• Task notification emails have US date format in them?

Fixed in

• Windows SharePoint Services 3.0 hotfix package (Sts.msp): October 28, 2008
• December Cumulative Update for MOSS2007 and WSS3 (Dec 17th 2008)
• Subsequent CU’s
• WSS3 SP2 (April 24th 2009)