There are attributes on xsl:sort that control the sorting:
order='ascending|descending'
This controls which way the sort is returned and defaults to 'ascending'.
case-order='upper-first|lower-first'
Defines which case is first and the default is language dependent.
lang='' controls the language of the sort (e.g. French).
data-type='text|number' controls when the data is treated as text or a number.
This can also be a QName to specify processor-specific sorting.
The default is 'text'.