Text domain not loading in constructor

I’m struggeling with this for two days, and Google, nor my “WordPress Plugin Development” handbook can help me. I’m really out of options.

Summarized, I’m building a (FAQ) plugin and I have trouble loading the text domain.
If I load it the ‘traditional’ functional way, it works fine.
If I put it in the constructor of a class, it fails.
The code below is trimmed to loading the text domain only, but the same constructor also creates a custom post type and a custom taxonomy, and that works just fine. So the problem in the constructor is restricted to loading the text domain only.

For your perception: This is the first time that I build a plugin the OO way. So it is also quite possible that I have an error in my code. However I haven’t found it yet.

This works fine (functional method):

/** Load text domain */
add_action('plugins_loaded', 'wdfaq_load_textdomain');

function wdfaq_load_textdomain() {
load_plugin_textdomain( 'wd-faq', false, dirname( plugin_basename(__FILE__) ) . '/languages/' );
}

This doesn’t load the text domain (OO method):

class wd_faq {	

	/** Constructor */
	public function __construct() {
		add_action('plugins_loaded', array($this,'wdfaq_load_textdomain'), 0 ); // Load text domain
	}

	/** Load text domain */
	public function wdfaq_load_textdomain() {
		load_plugin_textdomain( 'wd-faq', false, dirname( plugin_basename(__FILE__) ) . '/languages/' );
	}
}
$faq = new wd_faq();

Neither does this (OO method simplified):

class wd_faq {	

	/** Constructor */
	public function __construct() {
		load_plugin_textdomain( 'wd-faq', false, dirname( plugin_basename(__FILE__) ) . '/languages/' );
	}
}
$faq = new wd_faq();

I have checked the file names and they are OK:
wd-faq-en_US.mo
wd-faq-nl_NL.mo

(Btw, if they were not OK, the functional method would fail too of course)