Add ltr.css support for RTL-based multilingual sites

src/wp-includes/class-wp-styles.php

@@ -272,6 +272,34 @@ public function do_item( $handle, $group = false ) {
 			}
 		}
 
+		if ( 'rtl' !== $this->text_direction && isset( $obj->extra['ltr'] ) && $obj->extra['ltr'] ) {
+			if ( is_bool( $obj->extra['ltr'] ) || 'replace' === $obj->extra['ltr'] ) {
+				$suffix   = isset( $obj->extra['suffix'] ) ? $obj->extra['suffix'] : '';
+				$ltr_href = str_replace( "{$suffix}.css", "-ltr{$suffix}.css", $this->_css_href( $src, $ver, "$handle-ltr" ) );
+			} else {
+				$ltr_href = $this->_css_href( $obj->extra['ltr'], $ver, "$handle-ltr" );
+			}
+
+			$ltr_tag = sprintf(
+				"<link rel='%s' id='%s-ltr-css'%s href='%s'%s media='%s' />\n",
+				$rel,
+				esc_attr( $handle ),
+				$title ? sprintf( " title='%s'", esc_attr( $title ) ) : '',
+				$ltr_href,
+				$this->type_attr,
+				esc_attr( $media )
+			);
+
+			/** This filter is documented in wp-includes/class-wp-styles.php */
+			$ltr_tag = apply_filters( 'style_loader_tag', $ltr_tag, $handle, $ltr_href, $media );
+
+			if ( 'replace' === $obj->extra['ltr'] ) {
+				$tag = $ltr_tag;
+			} else {
+				$tag .= $ltr_tag;
+			}
+		}
+
 		if ( $this->do_concat ) {
 			$this->print_html .= $tag;
 			if ( $inline_style_tag ) {

tests/phpunit/tests/dependencies/stylesLTRSupport.php

@@ -0,0 +1,98 @@
+<?php
+/**
+ * @group dependencies
+ * @group i18n
+ */
+class Tests_Dependencies_StylesLtrSupport extends WP_UnitTestCase {
+
+	public function set_up(): void {
+		parent::set_up();
+		switch_to_locale( 'fa_IR' ); // RTL language.
+		wp_styles()->registered = array();
+	}
+
+	public function tear_down(): void {
+		restore_previous_locale();
+		parent::tear_down();
+	}
+
+	/**
+	 * @ticket 64193
+	 */
+	public function test_ltr_css_replace_data_is_set() {
+		$handle = 'sample-style';
+		wp_register_style( $handle, 'https://example.com/style.css' );
+		wp_style_add_data( $handle, 'ltr', 'replace' );
+
+		$styles = wp_styles();
+		$this->assertArrayHasKey( 'ltr', $styles->registered[ $handle ]->extra );
+		$this->assertSame( 'replace', $styles->registered[ $handle ]->extra['ltr'] );
+	}
+
+	/**
+	 * @ticket 64193
+	 */
+	public function test_ltr_css_suffix_data_is_set() {
+		$handle = 'sample-style-suffix';
+		wp_register_style( $handle, 'https://example.com/style.min.css' );
+		wp_style_add_data( $handle, 'ltr', 'suffix' );
+
+		$styles = wp_styles();
+		$this->assertArrayHasKey( 'ltr', $styles->registered[ $handle ]->extra );
+		$this->assertSame( 'suffix', $styles->registered[ $handle ]->extra['ltr'] );
+	}
+
+	/**
+	 * @ticket 64193
+	 */
+	public function test_no_ltr_data_for_ltr_locale() {
+		restore_previous_locale();
+		switch_to_locale( 'en_US' ); // LTR language.
+
+		$handle = 'sample-style-ltr';
+		wp_register_style( $handle, 'https://example.com/style.css' );
+		wp_style_add_data( $handle, 'ltr', 'replace' );
+
+		$styles = wp_styles();
+		$this->assertArrayHasKey( 'ltr', $styles->registered[ $handle ]->extra );
+		$this->assertSame( 'replace', $styles->registered[ $handle ]->extra['ltr'] );
+	}
+	/**
+	 * Verify that an LTR stylesheet actually gets printed in HTML output.
+	 *
+	 * @group output
+	 * @ticket 64193
+	 */
+	public function test_ltr_stylesheet_is_printed_in_output() {
+		$this->setExpectedDeprecated( 'print_emoji_styles' );
+
+		global $wp_styles;
+
+		// Reset styles registry to ensure a clean environment.
+		$wp_styles = null;
+		wp_styles();
+
+		// Register main style.
+		wp_register_style( 'ltr-test-style', 'http://example.com/css/style.css', array(), '1.0' );
+
+		// Mark this style as having an LTR variant.
+		wp_style_add_data( 'ltr-test-style', 'ltr', true );
+
+		// Enqueue the style.
+		wp_enqueue_style( 'ltr-test-style' );
+
+		// Capture printed output.
+		ob_start();
+		wp_print_styles();
+		$output = ob_get_clean();
+
+		// Assertions.
+		$this->assertStringContainsString( 'style.css', $output, 'Main stylesheet was not printed in output.' );
+		$this->assertStringContainsString( 'ltr.css', $output, 'LTR stylesheet was not printed in output.' );
+
+		// Verify correct order (LTR after main style).
+		$main_pos = strpos( $output, 'style.css' );
+		$ltr_pos  = strpos( $output, 'ltr.css' );
+		$this->assertTrue( $ltr_pos > $main_pos, 'LTR stylesheet should appear after the main style.' );
+	}
+}