Translate WooCommerce and WooCommerce Germanized mails into order language with TranslatePress before sending. Note: As of TranslatePress Version 2.3.5, this functionality was implemented natively by TranslatePress, making this Code obsolete. Read more here: https://translatepress.com/docs/translating-woocommerce-emails/

functions.php

// Save the current language in post_meta when checkout is processed (used to identify correct Email language)
add_action('woocommerce_checkout_update_order_meta', 'dartrax_save_language_on_checkout', 10, 2 );
function dartrax_save_language_on_checkout( $order_id, $posted ) {
	if( ! class_exists('TRP_Translate_Press') ) return '';
	global $TRP_LANGUAGE;
    update_post_meta( $order_id, 'order_language', $TRP_LANGUAGE );
}

// Woocommerce Germanized Mails
add_action( 'woocommerce_gzd_shipment_status_draft_to_shipped_notification', 'dartrax_prepare_locale_for_Mail_with_shipment_id', 5, 1 );
add_action( 'woocommerce_gzd_shipment_status_processing_to_shipped_notification', 'dartrax_prepare_locale_for_Mail_with_shipment_id', 5, 1 );
add_action( 'woocommerce_gzd_return_shipment_status_draft_to_processing_notification', 'dartrax_prepare_locale_for_Mail_with_shipment_id', 5, 1 );
add_action( 'woocommerce_gzd_return_shipment_status_requested_to_processing_notification', 'dartrax_prepare_locale_for_Mail_with_shipment_id', 5, 1 );
add_action( 'woocommerce_gzd_return_shipment_status_processing_to_delivered_notification', 'dartrax_prepare_locale_for_Mail_with_shipment_id', 5, 1 );
add_action( 'woocommerce_gzd_return_shipment_status_shipped_to_delivered_notification', 'dartrax_prepare_locale_for_Mail_with_shipment_id', 5, 1 );
function dartrax_prepare_locale_for_Mail_with_shipment_id( $shipment_id ) {
	// get order_id from shipment and proceed with that
	if( $shipment = wc_gzd_get_shipment( $shipment_id ) )
		dartrax_prepare_locale_for_Mail_with_order_id( $shipment->get_order_id() );
}

// Woocommerce Shipment Mails
add_action( 'woocommerce_order_status_processing_to_cancelled_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_on-hold_to_cancelled_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_completed_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_pending_to_on-hold_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_failed_to_on-hold_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_cancelled_to_on-hold_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_cancelled_to_processing_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_failed_to_processing_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_on-hold_to_processing_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_pending_to_processing_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_fully_refunded_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_partially_refunded_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_pending_to_failed_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_on-hold_to_failed_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_pending_to_completed_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_failed_to_completed_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
add_action( 'woocommerce_order_status_cancelled_to_completed_notification','dartrax_prepare_locale_for_Mail_with_order_id', 5, 1 );
function dartrax_prepare_locale_for_Mail_with_order_id( $order_id ) {
	// Get language code that may be stored in post meta data
	$lang_code = get_post_meta($order_id, 'order_language', true);
	if( $lang_code == '' || ! class_exists('TRP_Translate_Press') ) return '';
	// Set it as current active language for translatepress
	global $TRP_LANGUAGE;
	$TRP_LANGUAGE = $lang_code;
}

// Woocommerce Mails when resend by Admin
add_action( 'woocommerce_before_resend_order_emails','dartrax_prepare_locale_for_resend_Mails', 5, 2 );
function dartrax_prepare_locale_for_resend_Mails( $order, $mail_type ) {
	// First type belongs to WooCommerce, last two types belong to WooCommerce Germanized
	if($mail_type == 'customer_invoice' || $mail_type == 'customer_paid_for_order' || $mail_type == 'customer_processing_order')
		dartrax_prepare_locale_for_Mail_with_order_id( $order->get_id() );
}

// Woocommerce Note to customer Mail
add_action( 'woocommerce_new_customer_note_notification','dartrax_prepare_locale_for_note_Mails', 5, 1 );
function dartrax_prepare_locale_for_note_Mails( $note_and_order_id ) {
	// get order_id from argument array and proceed with that
	dartrax_prepare_locale_for_Mail_with_order_id( $note_and_order_id['order_id'] );
}

// Prevent Woocommerce Germanized from filtering the Translatepress Shortcut when legal pages are used in emails
add_filter( 'woocommerce_gzd_email_attachment_content_shortcodes_allowed', function( $shortcodes_allowed ) {
	array_push($shortcodes_allowed, "trp_language");
	return $shortcodes_allowed;
} );

// Override Locale when WooCommerce sends an eMail
add_filter( 'woocommerce_email_setup_locale', function() {
	if( ! class_exists('TRP_Translate_Press') ) return '';
	// Override translatepress 'locale'-function because that does not work in Admin interface
	add_filter('locale','dartrax_force_trp_locale', 99999 + 1);
	// Switch text domains to load the correct .po/.mo-file based translations
	global $TRP_LANGUAGE;
	switch_text_domains( $TRP_LANGUAGE );
	return false;
} );
add_filter( 'woocommerce_email_restore_locale', function() {
	// Undo overriding of translatepress' 'locale'-function
	remove_filter('locale','dartrax_force_trp_locale', 99999 + 1);
	return true;
} );

// Override translatepress 'locale'-function because that does not deliver $TRP_LANGUAGE in Admin interface
function dartrax_force_trp_locale($locale) {
	global $TRP_LANGUAGE;
	return $TRP_LANGUAGE;
}	

// Override 'plugin_locale'-function so Woocommerce and Woocommerze Germanized won't use the admin profile language
function dartrax_force_woo_locale($locale, $plugin) {
	global $TRP_LANGUAGE;
	return $plugin == 'woocommerce' || $plugin == 'woocommerce-germanized' ? $TRP_LANGUAGE : $locale;
}

// Switch to another text domain. Inspired by https://gist.github.com/Jon007/5b90e78289899bc28e9c39c12ef56e60
function switch_text_domains( $language ) {
	if ( class_exists( 'TRP_Translate_Press' ) && class_exists( 'WooCommerce' ) && class_exists( 'WooCommerce_Germanized' ) ) {
		global $locale, $woocommerce, $woocommerce_germanized;
		// unload plugin's textdomains
		unload_textdomain( 'default' );
		unload_textdomain( 'woocommerce' );
		unload_textdomain( 'woocommerce-germanized' );
		// set locale to order locale
		$locale	= apply_filters( 'locale', $language );
		// Woocommerce and Woocommerce Germanized use the admin profile language instead of the side language. Override with the desired language
		add_filter('plugin_locale', 'dartrax_force_woo_locale', 10, 2);
		// (re-)load plugin's textdomain with order locale
		load_default_textdomain( $language );
		$woocommerce->load_plugin_textdomain();
		$woocommerce_germanized->load_plugin_textdomain();
		$wp_locale = new \WP_Locale();
		// Clean up
		remove_filter('plugin_locale', 'dartrax_force_woo_locale', 10);		
	}
}

Thanks @dartrax , it seems that actual admin user language somehow overwrites the order_language field. If I set my admin profile to German everything is sent in German, but once it's English it is sending everything (instead of the first email) in English, however the order was made on the German site. At least, error log is now OK.

[14-Feb-2022 13:53:10 UTC] switch to en_US start
[14-Feb-2022 13:53:10 UTC] locale is de_DE
[14-Feb-2022 13:53:10 UTC] language gets filtered to en_US
[14-Feb-2022 13:53:10 UTC] switch to en_US end

it seems that actual admin user language somehow overwrites the order_language field.

Hi @Nieder-hu,
by "somehow overwrites" do you mean that it actually changes its value in the Database?
The order_language field is the place where the language used by the user who checks out an order is stored. It should only be read and written by my code above. Do you have any other plugin, like wpml or woocommerce multilingual that also uses this parameter? You can do a search and replace in the code of this gist and use any other name, like "dartrax_order_language" instead of "order_language" to rule out any conflict.

Please check if that parameter is set to "de_DE" for the order in question first.

If that's the case, the Log should read:

[14-Feb-2022 13:53:10 UTC] switch to de_DE start
[14-Feb-2022 13:53:10 UTC] locale is en_US
[14-Feb-2022 13:53:10 UTC] language gets filtered to de_DE
[14-Feb-2022 13:53:10 UTC] switch to de_DE end

...and not the other way around!

If I set my admin profile to German everything is sent in German

So the translation files are there. Good to have that checked!

Hi @dartrax ,
no, the meta field value is unchanged (de_DE). Even if I change its name to something else in the code, it doesn't change. The main language is German, but I use the wp admin interface in English. So I got a nice log, that says everything should be totally German, but in reality, emails are sent in English. I tried to deactivate all the plugins and so on but nothing works so far. Also tried to set order language to en_US and switch wp admin to German. In that case, emails are German. I really appreciate your help, because I'm totally lost about what could be wrong.

[15-Feb-2022 04:26:17 UTC] switch to de_DE start
[15-Feb-2022 04:26:17 UTC] locale is de_DE
[15-Feb-2022 04:26:17 UTC] language gets filtered to de_DE
[15-Feb-2022 04:26:17 UTC] switch to de_DE end

Hi @Nieder-hu,
I‘d like to make a test environment with the same settings as you have to see if I can reproduce that issue. Can you give me the following information:

Wordpress Version
Woocommerce Version
Translatepress Version
Translatepress Business Version if installed
Germanized Version
Wordpress Main language in general settings
Admin user language in user profile

I‘m not sure if it has something to do with different Page default/Admin languages (a case that I did not test yet) or with plugin versions (I still use Woocommerce 5.x).

Hi @dartrax , thanks for your help.

WordPress version: 5.9
WooCommerce version: 6.2.0
TranslatePress - Developer: 1.0.9
TranslatePress - Multilingual: 2.2.0
Germanized for WooCommerce: 3.83.
WP main language: German (de_DE)
Admin language: English (en_US)

Hi @Nieder-hu,
finally I was able to reproduce your issue. The culprit is the admin user locale not being the sites default locale. The function $woocommerce->load_plugin_textdomain() uses determine_locale(), which returns the user locale if the user is the admin user instead of the site default locale (which was set to the order_language before). I've added a filter to the plugin_locale hook, please tell me if that fixes your problem.

Fix: When the admin profile language did not match the side default language, instead of the order language the admin profile language was used for the translations covered by the woocommerce .mo/.po-files.

Hi @dartrax , thanks it works well.

Fix: Since a recent update of WooCommerce Germanized, the trp_language conditional shortcode got ignored when used in legal pages included with mails. This resulted in mails in which, for example, the terms and conditions occurred several times in a row in all available languages. This is fixed now.

For everyone's interest:
I've used the new Mail localisation feature that was natively build into TranslatePress for a while now, and I did not encounter any problems.

Just this little peace of code is still necessary, if you want to use the TranslatePress' conditional shortcuts in Emails, because otherwise they get filtered by the Germanized Extension.

// Prevent Woocommerce Germanized from filtering the Translatepress Shortcut when legal pages are used in emails
add_filter( 'woocommerce_gzd_email_attachment_content_shortcodes_allowed', function( $shortcodes_allowed ) {
	array_push($shortcodes_allowed, "trp_language");
	return $shortcodes_allowed;
} );