Markup fix

Doc/lib/libgettext.tex

@@ -102,9 +102,9 @@ If no translation is found, return \var{singular} if \var{n} is 1;
 return \var{plural} otherwise.
 
 The Plural formula is taken from the catalog header. It is a C or
-Python expression that has a free variable n; the expression evaluates
+Python expression that has a free variable \var{n}; the expression evaluates
 to the index of the plural in the catalog. See the GNU gettext
-documentation for the precise syntax to be used in .po files, and the
+documentation for the precise syntax to be used in \file{.po} files and the
 formulas for a variety of languages.
 
 \versionadded{2.3}