So, is there a way to set the decimal format based on the content of
the XML with all docs being generated in an single locale?

You need to define two decimal formats e.g.
  <xsl:decimal-format
    name="d1"
    decimal-separator="."
    grouping-separator=","/>

  <xsl:decimal-format
    name="d2"
    decimal-separator=","
    grouping-separator="."/>

then your code can choose e.g.
   <xsl:choose>
     <xsl:when test="Currency = 'Euro'">
       <xsl:value-of select="format-number(foo, '0.00', 'd2')"/>
     </xsl:choose>
     <xsl:otherwise>
       <xsl:value-of select="format-number(foo, '0.00'., 'd1')"/>
     </xsl:otherwise>
   </xsl:choose>

	Martin Honnen
	http://JavaScript.FAQTs.com/