__() & _e() do not support LANG attribute

They’re not supposed to, that’s not how they work. Those functions use the language defined in WordPress’ settings and get their translations from a translation file in the theme or plugin. See the Localization page of the Theme Developer Handbook for more.

If you’re using a static HTML attribute then you probably shouldn’t be using the translation functions at all, as the use of the attribute with a hard-coded value implies that the language won’t/can’t change.

• This reply was modified 6 years, 11 months ago by Jacob Peattie.

I know how to use i18n in WordPress. The problem is not the file, but the fact that in a site of a specific language, I have pages in other languages. So, in those pages, the same plug-in should use another language file. The problem is that I do not know how to FORCE the language in a specific page.

• This reply was modified 6 years, 11 months ago by dejudicibus.

SOLVED! I added this function to functions.php

if( ! function_exists('load_specific_textdomain') ){	
	function load_specific_textdomain( $textdomain = 'default', $locale = null ) {
		if ( null === $locale ) {
			$locale = is_admin() ? get_user_locale() : get_locale();
		}
	 
		// Unload previously loaded strings so we can switch translations.
		unload_textdomain( $textdomain );
	 
		$return = load_textdomain( $textdomain, WP_LANG_DIR . "/$locale.mo" );
	 
		if ( ( is_multisite() || ( defined( 'WP_INSTALLING_NETWORK' ) && WP_INSTALLING_NETWORK ) ) && ! file_exists(  WP_LANG_DIR . "/admin-$locale.mo" ) ) {
			load_textdomain( $textdomain, WP_LANG_DIR . "/ms-$locale.mo" );
			return $return;
		}
	 
		if ( is_admin() || wp_installing() || ( defined( 'WP_REPAIRING' ) && WP_REPAIRING ) ) {
			load_textdomain( $textdomain, WP_LANG_DIR . "/admin-$locale.mo" );
		}
	 
		if ( is_network_admin() || ( defined( 'WP_INSTALLING_NETWORK' ) && WP_INSTALLING_NETWORK ) )
			load_textdomain( $textdomain, WP_LANG_DIR . "/admin-network-$locale.mo" );
	 
		return $return;
	}
}

then I used the following block of code:

// $lang is the language you wish to temporarily load
// $domain is the text domain 
//       if $lang is null, use the current locale

if ($lang != null) {
	$clang = is_admin() ? get_user_locale() : get_locale();
	load_specific_textdomain($domain, $lang);
}

// Place here the code containing __($string_to_be_translated, $domain)

if ($lang != null) {
	load_specific_textdomain($domain, $clang);
}