For the past few days I have been trying to deal with the problem of translating emails. I have the following plugins installed: WooCommerce, WooCoomerce wFirma (it is for invoices, receipt and finances), Polylang for WooCommerce, WooCommerce Multilingual & Multicurrency, WPML for Polylang and Loco Translate. All email templates from WooCommerce -> Settings -> Email are in English (title, header and content in PHP), in addition, in the Email tab I also have emails from the wFirma plugin, which look more or less like this:

<?php do_action( 'woocommerce_email_header', $email_heading, $email ); ?>

<b><?php printf( __('Please find attached an invoice for your order %s.', 'woocommerce-wfirma'), $order->get_order_number() ); ?></b><br/><br/>
<?php
if( isset( $download_url ) ) {
	printf( __('Receipt for order: <a href="%s"><b>Download PDF.</b></a>', 'woocommerce-wfirma'), $download_url );
	echo '<br/><br/>';
} ?>
<h2><?php echo __( 'Order #', 'woocommerce' ) . $order->get_order_number(); ?> (<?php printf( '<time datetime="%s">%s</time>', date_i18n( 'c', strtotime( $order->get_date_created() ) ), date_i18n( wc_date_format(), strtotime( $order->get_date_created() ) ) ); ?>)</h2>

<table cellspacing="0" cellpadding="6" style="width: 100%; border: 1px solid #eee;" border="1" bordercolor="#eee">
	<thead>
	<tr>
		<th scope="col" style="text-align:left; border: 1px solid #eee;"><?php _e( 'Product', 'woocommerce' ); ?></th>
		<th scope="col" style="text-align:left; border: 1px solid #eee;"><?php _e( 'Quantity', 'woocommerce' ); ?></th>
		<th scope="col" style="text-align:left; border: 1px solid #eee;"><?php _e( 'Price', 'woocommerce' ); ?></th>
	</tr>
	</thead>
	<tbody>
	<?php
	switch ( $order->get_status() ) {
		case "completed" :
			if ( version_compare( WC_VERSION, '3.0', '<' ) ) {
				echo $order->email_order_items_table(array());
			}
			else {
				echo wc_get_email_order_items( $order);
			}
			break;
		case "processing" :
			if ( version_compare( WC_VERSION, '3.0', '<' ) ) {
				echo $order->email_order_items_table(array());
			}
			else {
				echo wc_get_email_order_items( $order);
			}
			break;
		default :
			if ( version_compare( WC_VERSION, '3.0', '<' ) ) {
				echo $order->email_order_items_table(array());
			}
			else {
				echo wc_get_email_order_items( $order);
			}
			break;
	}
	?>
	</tbody>
	<tfoot>
	<?php
	if ( $totals = $order->get_order_item_totals() ) {
		$i = 0;
		foreach ( $totals as $total ) {
			$i++;
			?><tr>
			<th scope="row" colspan="2" style="text-align:left; border: 1px solid #eee; <?php if ( $i == 1 ) echo 'border-top-width: 4px;'; ?>"><?php echo $total['label']; ?></th>
			<td style="text-align:left; border: 1px solid #eee; <?php if ( $i == 1 ) echo 'border-top-width: 4px;'; ?>"><?php echo $total['value']; ?></td>
			</tr><?php
		}
	}
	?>
	</tfoot>
</table>

<?php do_action( 'woocommerce_email_after_order_table', $order, $sent_to_admin, $plain_text, $email ); ?>

<?php do_action( 'woocommerce_email_order_meta', $order, $sent_to_admin, $plain_text, $email ) ?>

<h2><?php _e( 'Customer details', 'woocommerce' ); ?></h2>

<?php if ( $order->get_billing_email() ) : ?>
	<p><strong><?php _e( 'Email:', 'woocommerce' ); ?></strong> <?php echo $order->get_billing_email(); ?></p>
<?php endif; ?>
<?php if ( $order->get_billing_phone() ) : ?>
	<p><strong><?php _e( 'Tel:', 'woocommerce' ); ?></strong> <?php echo $order->get_billing_phone(); ?></p>
<?php endif; ?>

<?php wc_get_template( 'emails/email-addresses.php', array( 'order' => $order ) ); ?>

<?php do_action( 'woocommerce_email_footer' ); ?>

In the standard they were in Polish, but I changed them to English everywhere. In addition, I used Loco Translate to translate everything that can be used in these emails (on the Woo and wFirma side). In the WordPress settings, I set the default language as English (UK).

The problem is that when a user enters the homepage, selects a language (Polish or English) and makes a purchase, I get an email in the appropriate language, while each subsequent one, e.g. from wFirma, is only in English (including the email title), and each subsequent one from WooCommerce has only the email title, header translated, while the content is in English.

Has anyone encountered this problem before and knows where to look for the cause?

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