function language_switcher_fun( $atts ){
	ob_start();
	do_action('wpml_add_language_selector');
	return ob_get_clean();
}
add_shortcode( 'language_switcher_shortcode', 'language_switcher_fun' );
Code language: PHP (php)

The do_action('wpml_add_language_selector'); action outputs the language switcher based on the options set in the Custom Language Switchers section in WPML ? Languages.

You can use it like this [language_switcher_shortcode]