This is a workaround. Without this patch, export to .tex (XeTeX)
contains a sequence such as
\begin{english}
\begin{description}
[omitted, but does not contain \end{description}]
\end{english}
Thanks to Jürgen for the workaround.
\end_layout
\begin_layout Description
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+\end_layout
+
+\end_inset
+
\lang english
TeX
\end_layout
\begin_layout Description
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+\end_layout
+
+\end_inset
+
\lang english
LaTeX
\end_layout
\begin_layout Description
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+\end_layout
+
+\end_inset
+
\lang english
LyX
\end_layout
\begin_layout Itemize
+\begin_inset ERT
+status open
+
+\begin_layout Plain Layout
+
+\end_layout
+
+\end_inset
+
\family sans
\lang english