Inheritance of customized generated text

["honyk" <j.tosovsky@email.cz>]

For two my projects I would like to share customized gentext and after
importing this customization layer into next customization layer to perform
additional changes to gentext, relative to appropriate project. I found
difficult to set it out properly. 
If in db-common.xsl following changes are specified:
   <i18n xmlns="http://docbook.sourceforge.net/xmlns/l10n/1.0";>
      <l10n language="en">
         <context name="title">
            <template name="example" text="Example %t"/>
            <template name="informalexample" text="Example"/>
         </context>
      </l10n>
   </i18n>

and this layer is later imported using <xsl:import href="db-common.xsl"/>
into next layer with following code:
   <xsl:param name="local.l10n.xml" select="document('')"/> 
   <i18n xmlns="http://docbook.sourceforge.net/xmlns/l10n/1.0";>
      <l10n language="en">
         <context name="title">
            <template name="example" text="%t"/>
         </context>
      </l10n>
   </i18n>

It seems all db-common changes are ignored and only these from second layer
are used (i.e. informalexample is unknown). My list of changes is much
larger so it is quite important. Is there any mistake in my code or
different approach should be used instead?