Try this way:
string ms:format-date(string datetime, string format [,locale])
This will work for you:
<xsl:value-of select="ms:format-date(., 'dd/MM/yyyy')" xmlns:xsl="#unknown" />
Refer DateFormats:
http://msdn.microsoft.com/en-us/library/ms256099.aspx[
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Have a look on example:
XSLT DateTime Formatting[
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And a similar example to your question:
xsl format date dd/MM/yyyy[
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Also check this one:
Formatting Dates and Times[
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Here three functions are provided to represent dates and times as a string, using the conventions of a selected calendar, language, and country.