DOCBOOK-APPS: getting uppercase.alpha from gentext

[David Cramer <david_cramer@broadjump.com>]

When I add this to my customization layer (in an effort to convert any
text inside <keycaps> to uppercase:

  <xsl:template match="keycap">
	<xsl:variable name="uppercase.alpha">
	  <xsl:call-template name="gentext">
		<xsl:with-param name="key" select="'uppercase.alpha'"/>
	  </xsl:call-template>
	</xsl:variable>
	<xsl:variable name="lowercase.alpha">
	  <xsl:call-template name="gentext">
		<xsl:with-param name="key" select="'lowercase.alpha'"/>
	  </xsl:call-template>
	</xsl:variable>
	<xsl:value-of 
	  select="translate(., 
	  $lowercase.alpha, 
	  $uppercase.alpha)"/>
	<!--xsl:call-template name="inline.charseq"/-->
  </xsl:template>

I get the warning:

'No "en" localization of "uppercase.alpha" exists; using "en".
No "en" localization of "lowercase.alpha" exists; using "en".' 

In doing this, I'm simply copying what I see in elsewhere in the
stylesheets (e.g. labels.xsl):

    <xsl:when test="$deflabel = 'qanda' and local-name(.) = 'answer'">
      <xsl:call-template name="gentext">
        <xsl:with-param name="key" select="'Answer'"/>
      </xsl:call-template>
    </xsl:when>

If I add replace uppercase.alpha with Answer in the with-param it does
work. What's different about uppercase.alpha and lowercase.alpha? Can
anybody see something I'm doing wrong?

Thanks,
David