doc: describe how to choose the language (i18n) at run time

Removed the current section from 'INSTALL-WMAKER' and wrote an updated
chapter in the new README.i18n, to explain how the language is chosen at
run-time.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

doc/build/Translations.texi

@@ -80,6 +80,7 @@ This manual is for Window Maker, version @value{version}.
 
 @menu
 * Enabling Languages support::  How to compile Window Maker with i18n support
+* Choosing the Language::       When installed, how to run wmaker with your language
 @end menu
 
 
@@ -127,5 +128,64 @@ Please note that if you also specify a value on the command line, it will have p
 value in that file.
 
 
+@c ----------------------------------------------------------------------- Choosing the Language ---
+@node Choosing the Language
+@chapter Choosing the Language
+
+If you have compiled and installed @sc{Window Maker} with support for your language,
+the effective translation is done is the very same way as any other application on an @sc{Unix}
+system, you just have to set the shell variable @env{LANG} to your language before @command{wmaker}
+is started.
+In @command{sh} type of shell (@sc{sh}, @sc{ksh}, @sc{bash}, ...), this is done for example with
+(@code{fr} is for French):
+
+@example
+export LANG=fr
+@end example
+
+
+There is also a command line option @option{--locale} for @sc{Window Maker} which may be used to set
+the language:
+
+@example
+wmaker --locale fr
+@end example
+
+When using this option, @sc{Window Maker} will use the locale you specified, redefining the
+@env{LANG} environment variable to this value so all program started from @sc{Window Maker} will
+inherit its value.
+
+
+If your system is using @sc{systemd}, you can also configure the locale at system level using the
+command:
+
+@example
+localectl set-locale LANG=fr
+@end example
+
+
+You can check if the current value is properly supported with the command:
+
+@example
+locale
+@end example
+
+If this does not work, you may need first to activate the support for your locale in the system;
+you can get the list of currently enabled locales with the command:
+
+@example
+locale -a
+@end example
+
+You should be able to enable a new language support by editing the file @file{/etc/locale.gen} to
+uncomment the locale(s) you need (by removing the @code{#} character and space(s) in front of it,
+and by running the command @command{locale-gen} as root.
+
+For further information, you may wish to read dedicated documentation, for example from
+@uref{http://tldp.org/HOWTO/HOWTO-INDEX/other-lang.html, the Linux Documentation Project}
+or through pages like
+@uref{http://www.shellhacks.com/en/HowTo-Change-Locale-Language-and-Character-Set-in-Linux,Shell Hacks' note on Changing Locale}.
+
+
 @c ------------------------------------------------------------------------------------- The End ---
 @bye