Michel - xiligroup dev on "[Plugin: Jetpack by WordPress.com] Jetpack not correctly translated by multilingual plugins"

Habemus exsarcio, there is a workaround
I encountered this same problem with bbPress in september - a too early firing to set localization...
Because it is long to obtain a fixe by the authors (delays).
The solution is based on unload_textdomain and two filters : the case jetpack is here added in bbPress solution. (xili-language plugin is compatible to a multilingual bbPress forum.
This code is here provided as example:

function xili_xl_bbp_lang_init ( ) {
	if ( is_admin() )

		add_filter( 'plugin_locale', 'xili_bbp_admin_side_locale', 10, 2);
}

function xili_bbp_admin_side_locale ( $locale = 'en_US', $domain = 'bbpress' ) {
	if ( in_array ( $domain, array( 'bbpress' , 'jetpack' ) ) ) {

		$locale = get_user_option( 'user_locale' );  // set elsewhere in xililanguage

			if ( empty( $locale ) ) {
				$locale = ( defined( 'WPLANG' ) ) ? WPLANG : 'en_US';

				if ( is_multisite() ) {
					if ( defined( 'WP_INSTALLING' ) || ( false === $ms_locale = get_option( 'WPLANG' ) ) )
						$ms_locale = get_site_option( 'WPLANG' );

				if ( $ms_locale !== false )
						$locale = $ms_locale;
				}
			}
			// example for jetpack
			unload_textdomain( 'jetpack' );
			load_textdomain( 'jetpack', WP_PLUGIN_DIR.'/jetpack/languages/jetpack-'.$locale.'.mo' );
	}

	return $locale;
}
add_action( 'plugins_loaded', 'xili_xl_bbp_lang_init', 9 ); // 9 = to be registered before bbPress instantiate

With these few lines, webmaster in the admin side is able to choose 'live' his language.

M.