Wp internationalization not loaderd

I have problem with loading internationalization in my admin page. For generating .po and .mo files i use Poedit.

My plugin structure is simple:

├───plugins
│   └───radni
│        └───radni.php
│        └───lang
│              └───radni-sr_RS.mo
│              └───radni-sr_RS.po

Plugin header:

/**
 * Plugin Name: Radni
 *
 * Text Domain: radni
 * Domain Path: /lang/
 */

Load hooks:

add_action( 'init', 'myplugin_init' );

Also i try hook 'plugins_loaded'

Then callback

function myplugin_init()
{
    load_plugin_textdomain( 'radni', false, dirname( plugin_basename( __FILE__ ) ) . '/lang');
}

And set in wp-config.php

define('WPLANG', 'sr_RS');

I use __('','') and _e('','') but nothing is translated.

I try to make debug:

function my_i18n_debug(){

    $loaded=load_plugin_textdomain( 'radni', false, dirname( plugin_basename( __FILE__ ) ) . '/lang');

    if ( ! $loaded ){

        echo "<hr/>";

        echo "Error: the mo file was not found! ";

        exit();

    }else{

        echo "<hr/>Debug info:<br/>";

        echo "WPLANG: ". WPLANG;

        echo "<br/>";

        echo "translate test: ". __('Some text','radni');

        exit();

    }
}

Error: the mo file was not found!

What i do wrong i read all docs from wp and nothing is changed!!!