The WPML constant ICL_LANGUAGE_NAME and others are deprecated in WPML v4.6.7. This is a replacement template function for that and more.

wpml_get_current_language_name.php

<?php
if ( ! function_exists( 'wpml_get_current_language_name' ) ) :
	/**
	 * Returns current active site language array.
	 * If the optional $arg is set, only the corresponding value is returned.
	 * 
	 * $arg can be one of: 
	 * code, id, native_name, major, active, default_locale, 
	 * encode_url, tag, translated_name, url, country_flag_url, language_code
	 */
	function wpml_get_current_language( $arg = NULL ){
		$wpml_active_languages = apply_filters( 'wpml_active_languages', NULL, NULL );
		if ( !is_array( $wpml_active_languages ) ) {
			return null;
		}

		foreach ($wpml_active_languages as $key => $language) {
			if ( isset($language['active']) && $language['active'] == 1 ) {
				//return language array
				if(!$arg){
					return $language;
				}
				//return only selected language value
				//one of ["code"], ["id"], ["native_name"], ["major"], ["active"], ["default_locale"], ["encode_url"], ["tag"], ["translated_name"], ["url"], ["country_flag_url"], ["language_code"]
				if( $arg && isset($language[$arg]) ){
					return $language[$arg];
				}
			}
		}
		return null; //No active language
	}
endif;