add missing sentence

Co-authored-by: Henrik Tidefelt <henrikt@wolfram.com>

chapters/packages.tex

@@ -348,8 +348,8 @@ \section{Multilingual Descriptions}\label{multilingual-descriptions}
 The pattern \filename{$\mathit{language}$} stands for the ISO 639-1 language code, e.g., \filename{de} or \filename{en}.
 \end{enumerate}
 
-The files consist of a header and a body.
 The detailed format of these files is described in \href{https://www.gnu.org/software/gettext/manual/gettext.pdf}{GNU gettext}.
+For Modelica translations, only the keywords \lstinline!msgctxt!, \lstinline!msgid! and \lstinline!msgstr! are used.
 
 \begin{nonnormative}
 In the remainder of this section, several facts about the gettext specification are described non-normatively for easy access to some of the gettext basics.
@@ -359,6 +359,7 @@ \section{Multilingual Descriptions}\label{multilingual-descriptions}
 Comments start with an \lstinline!#! and are continued until the end of line.
 Spaces outside strings are ignored and used as separators.
 
+The files consist of a header and a body.
 The header is marked with an empty \lstinline!msgid! entry and looks like this:
 \begin{lstlisting}
 # SOME DESCRIPTIVE TITLE.