hi
go to your admin page
Configuration->Languages, select the default language

Hi :-)

by default piwigo use default browser language

you can desactivate fonction to add local config


$conf['browser_language'] = false;

1/ go to administration -> plugins -> Manage
active [extension by Piwigo Team] LocalFiles Editor

2/ go to administration -> plugins -> LocalFile editor -> Tab 'local config'

paste

<?php
$conf['browser_language'] = false;
?>