Insert this line at the top
xmlns:ddwrt="http://schemas.microsoft.com/WebParts/v2/DataView/runtime"

That will give you a header looking like this:

[xml]
<xsl:stylesheet
version="1.0"
exclude-result-prefixes="x d xsl msxsl cmswrt"
xmlns:x="http://www.w3.org/2001/XMLSchema"
xmlns:d="http://schemas.microsoft.com/sharepoint/dsp"
xmlns:cmswrt="http://schemas.microsoft.com/WebParts/v3/Publishing/runtime"
xmlns:ddwrt="http://schemas.microsoft.com/WebParts/v2/DataView/runtime"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:msxsl="urn:schemas-microsoft-com:xslt">
[/xml]

Then use the “ddwrt:FormatDate” to show the date i various ways:

<xsl:value-of select="ddwrt:FormatDate(@dato, 1030, 3)"/>
<xsl:value-of select="ddwrt:FormatDateTime(string(@Publiceret), 1030, 'dd. MMM. yyyy')"/>
<xsl:value-of select="ddwrt:FormatDate(string(@Dato), 1033, 7) "/>

List of all LCID’s : http://support.microsoft.com/default.aspx?id=221435
Custom date and time formats: http://msdn.microsoft.com/en-us/library/8kb3ddd4(v=vs.110).aspx

Formatflags
dateflags