Translation docs update: don't recommend 20-year-old gettext; use msginit

Warning about gettext versions earlier than 0.10.35 is pointless,
as even 0.10.35 is from 2001, and so old it isn't even available
on GNU mirrors anymore. We shall not recommend a specific version in
the first place.

The proper way to start a new translation is to use msginit to initialize
a .po file -- just copying the .pot leaves many fields to their default
values, which the translator would need to fill in manually (the
Plural-Forms: field in particular).

docs/doxygen/mainpages/translations.h

@@ -452,9 +452,11 @@ Here are the steps you should follow:
    you should already have it. Otherwise you can always retrieve it directly
    from the git repository:
    <a href="https://raw.githubusercontent.com/wxWidgets/wxWidgets/master/locale/wxstd.pot">locale/wxstd.pot</a>.
--# Rename it to <tt>XY.po</tt> where <tt>"XY"</tt> is the 2 letter
+-# Initialize an <tt>XY.po</tt> file for your language by using the command
+   <tt>msginit -l XY</tt> in the same folder where you placed <tt>wxstd.pot</tt>.
+   The <tt>"XY"</tt> is the 2 letter
    <a href="http://www.loc.gov/standards/iso639-2/php/English_list.php">ISO 639-2 language code</a>
-   for your language.
+   for your language. Initialization can be also done using e.g. Poedit (see next item).
 -# Translate the strings in this file using either your favourite text
    editor or a specialized tool such as Vaclav Slavik's excellent
    <a href="http://www.poedit.net/">poEdit</a> utility.