Replace text in xml node with some value

If you can guarantee that the input XML will only have single digits, you could achieve this with simple look-up tables, which return the name of either the cardinal number (one, two, three, etc) or the ordinal form of the number (Half, Third, Fourth, etc)

   <ref:cardinals>
      <ref:cardinal>One</ref:cardinal>
      <ref:cardinal>Two</ref:cardinal>
      <ref:cardinal>Three</ref:cardinal>
      ... and so on...
   </ref:cardinals>

   <ref:ordinals>
      <ref:ordinal>Half</ref:ordinal>
      <ref:ordinal>Third</ref:ordinal>
      ... and so on ...
   </ref:ordinals>

(Where the ref namespace would have to be declared at the top of the XSLT)

To look up values in these look-up tables, you could set up a variable which references the XSLT document itself

<xsl:variable name="cardinals" select="document('')/*/ref:cardinals"/>
<xsl:value-of select="$cardinals/ref:cardinal[position() = $numerator]"/>

(Where $numerator is a variable containing the top half of the fraction)

Here is a full XSLT document which can cope with all single digit fractions

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:ref="http://stackoverflow.com/users/723763/abdul-muqtadir">
   <xsl:output method="xml" indent="yes"/>

   <ref:cardinals>
      <ref:cardinal>One</ref:cardinal>
      <ref:cardinal>Two</ref:cardinal>
      <ref:cardinal>Three</ref:cardinal>
      <ref:cardinal>Four</ref:cardinal>
      <ref:cardinal>Five</ref:cardinal>
      <ref:cardinal>Six</ref:cardinal>
      <ref:cardinal>Seven</ref:cardinal>
      <ref:cardinal>Eight</ref:cardinal>
      <ref:cardinal>Nine</ref:cardinal>
   </ref:cardinals>

   <ref:ordinals>
      <ref:ordinal>Half</ref:ordinal>
      <ref:ordinal>Third</ref:ordinal>
      <ref:ordinal>Quarter</ref:ordinal>
      <ref:ordinal>Fifth</ref:ordinal>
      <ref:ordinal>Sixth</ref:ordinal>
      <ref:ordinal>Seventh</ref:ordinal>
      <ref:ordinal>Eigth</ref:ordinal>
      <ref:ordinal>Ninth</ref:ordinal>
   </ref:ordinals>

   <xsl:variable name="cardinals" select="document('')/*/ref:cardinals"/>
   <xsl:variable name="ordinals" select="document('')/*/ref:ordinals"/>

   <xsl:template match="Fraction">
      <xsl:variable name="numerator" select="number(substring-before(., '/'))"/>
      <xsl:variable name="denominater" select="number(substring-after(., '/'))"/>
      <xsl:copy>
         <xsl:value-of select="$cardinals/ref:cardinal[position() = $numerator]"/>
         <xsl:text> </xsl:text>
         <xsl:value-of select="$ordinals/ref:ordinal[position() = $denominater - 1]"/>
         <xsl:if test="$numerator != 1">s</xsl:if>
      </xsl:copy>
   </xsl:template>

   <xsl:template match="@*|node()">
      <xsl:copy>
         <xsl:apply-templates select="@*|node()"/>
      </xsl:copy>
   </xsl:template>
</xsl:stylesheet>

When applied to your input XML, the following XML is returned

<Fractions>
   <Fraction>One Third</Fraction>
   <Fraction>One Half</Fraction>
</Fractions>

Note that you may have to look at handling plurals better. For example, if you had 3/2 as a fraction, the above solution returns Three Halfs, and not Three Halves.

If there's only a few, then use templates like these:

<xsl:template match="Fraction/text()[.='1/2']">half</xsl:template>
<xsl:template match="Fraction/text()[.='1/3']">one-third</xsl:template>
etc..