Load custom WP Jetpack translations

functions.php

<?php

define('CHILD_DIR', get_stylesheet_directory());

/**
 * Load Jetpack translations from themes/<theme>/lang/jetpack-sr_RS.mo
 */
function my_theme_setup()
{
    unload_textdomain('jetpack');
    load_textdomain('jetpack', CHILD_DIR . '/lang/jetpack-sr_RS.mo');
}
add_action('after_setup_theme', 'my_theme_setup');