WIP Fix: Possible typo?

Or is this missing a-Umlaut by design? I added it optionally, I guess the ? should be removed, maybe ae-Variant should also be added?
diff --git a/xslt/epub2i5.xsl b/xslt/epub2i5.xsl
index 3e26107..b0b1de0 100644
--- a/xslt/epub2i5.xsl
+++ b/xslt/epub2i5.xsl
@@ -160,9 +160,9 @@
                 <xsl:value-of select="concat('[', $x, ']')"/>
             </xsl:when>
             <xsl:when
-                test="matches($untertitel, '([Rr]oman|[Ee]rzhlung(en)?|[Aa]nthologie|[Gg]eschichte(n)?|[Nn]ovelle)')">
+                test="matches($untertitel, '([Rr]oman|[Ee]rzä?hlung(en)?|[Aa]nthologie|[Gg]eschichte(n)?|[Nn]ovelle)')">
                 <xsl:value-of
-                    select="concat('[', replace(replace($untertitel, '.*?(((^|\P{L})\p{L}+)?([Rr]oman|[Ee]rzhlung(en)?|[Aa]nthologie|[Gg]eschichte(n)?|[Nn]ovelle)).*', '$1'), '\P{L}*(.+)', '$1'), ']')"
+                    select="concat('[', replace(replace($untertitel, '.*?(((^|\P{L})\p{L}+)?([Rr]oman|[Ee]rzä?hlung(en)?|[Aa]nthologie|[Gg]eschichte(n)?|[Nn]ovelle)).*', '$1'), '\P{L}*(.+)', '$1'), ']')"
                     />
             </xsl:when>
             <xsl:otherwise>