build: Set the XSL parameter through the command line instead of sed

Use the xsltproc --stringparam option instead of replacing it inside the
file.

buildlib/po4a_manpage.mak

@@ -35,12 +35,13 @@ apt-vendor.ent: ../apt-vendor.ent
 	cp -a ../apt-vendor.ent .
 
 manpage-style.xsl: ../manpage-style.xsl
-	sed "/<!-- LANGUAGE -->/ i\
-<xsl:param name=\"l10n.gentext.default.language\" select=\"'$(LC)'\" />" ../manpage-style.xsl > manpage-style.xsl
+	cp -a $< .
 
 $($(LOCAL)-LIST) :: % : %.xml $(STYLESHEET) $(INCLUDES)
 	echo Creating man page $@
-	$(XSLTPROC) -o $@ $(STYLESHEET) $< || exit 200 # why xsltproc doesn't respect the -o flag here???
+	$(XSLTPROC) \
+		--stringparam l10n.gentext.default.language $(LC) \
+		-o $@ $(STYLESHEET) $< || exit 200 # why xsltproc doesn't respect the -o flag here???
 	test -f $(subst .$(LC),,$@) || echo 'FIXME: xsltproc respects the -o flag now, workaround can be removed'
 	mv -f $(subst .$(LC),,$@) $@
 

doc/manpage-style.xsl

@@ -5,7 +5,6 @@
 <xsl:import href="/usr/share/xml/docbook/stylesheet/nwalsh/manpages/docbook.xsl" />
 
 <xsl:param name="man.output.encoding" select="'UTF-8'" />
-<!-- LANGUAGE -->
 
 <xsl:template match="email">&lt;<xsl:apply-templates/>&gt;</xsl:template>