I'm new into XSLT and I made an Xpath expression to find out if an element with a specific attribute has siblings with the same attribute values.
This is what I made and want to know if this is the right way do do it?

example xml:
<elementname>
    <ns1:langstring xml:lang="nl">Dutch description</ns1:langstring>
    <ns1:langstring xml:lang="nl">Another Dutch description</ns1:langstring>
    <ns1:langstring xml:lang="en">English description</ns1:langstring>
</elementname>

example xsl:
       <xsl:template match="ns1:langstring">
<xsl:if test="following-sibling::*[@xml:lang = current()/@xml:lang]">
           there is more than 1 element with the @xml:lang value <xsl:value-of select="@xml:lang" /> in element <xsl:value-of select="../name()" />
       </xsl:if>
    </xsl:template>

You can use any grouping method to find groups of elements with matching values (use <xsl:for-each-group> in XSLT 2.0, or Muenchian grouping in 1.0 - see http://www.jenitennison.com/xslt/grouping). Then display the grouping key for any group whose size is >1.

In 2.0:
<xsl:template match="elementname">
<xsl:for-each-group select="*" group-by="@xml:lang">
  <xsl:if test="count(current-group()) gt 1">
    There is >1 with key <xsl:value-of select="current-grouping-key()"/>
  </xsl:if>
</xsl:for-each-group>
</xsl:template>

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference