Add theme.json i18n mechanism and JSON file specifying which theme.json paths are translatable

lib/class-wp-theme-json-resolver.php

@@ -71,6 +71,85 @@ private static function get_from_file( $file_path ) {
 		return $config;
 	}
 
+	/**
+	 * Processes a tree from i18n-theme.json into a linear array
+	 * containing the a translatable path from theme.json and an array
+	 * of properties that are translatable.
+	 *
+	 * @param array $file_structure_partial A part of a theme.json i18n tree.
+	 * @param array $current_path           An array with a path on the theme.json i18n tree.
+	 *
+	 * @return array An array of arrays each one containing a translatable path and an array of properties that are translatable.
+	 */
+	private static function theme_json_i18_file_structure_to_preset_paths( $file_structure_partial, $current_path = array() ) {
+		$result = array();
+		foreach ( $file_structure_partial as $property => $partial_child ) {
+			if ( is_numeric( $property ) ) {
+				return array(
+					array(
+						'path'              => $current_path,
+						'translatable_keys' => $file_structure_partial,
+					),
+				);
+			}
+			$result = array_merge(
+				$result,
+				self::theme_json_i18_file_structure_to_preset_paths( $partial_child, array_merge( $current_path, array( $property ) ) )
+			);
+		}
+		return $result;
+	}
+
+	/**
+	 * Returns a data structure used in theme.json translation.
+	 *
+	 * @return array An array of theme.json paths that are translatable and the keys that are translatable
+	 */
+	private static function get_presets_to_translate() {
+		static $theme_json_i18n = null;
+		if ( null === $theme_json_i18n ) {
+			$file_structure  = self::get_from_file( __DIR__ . '/experimental-i18n-theme.json' );
+			$theme_json_i18n = self::theme_json_i18_file_structure_to_preset_paths( $file_structure );
+
+		}
+		return $theme_json_i18n;
+	}
+
+	/**
+	 * Translates a theme.json structure.
+	 *
+	 * @param array  $theme_json_structure A theme.json structure that is going to be translatable.
+	 * @param string $domain               Optional. Text domain. Unique identifier for retrieving translated strings.
+	 *                                     Default 'default'.
+	 */
+	private static function translate_presets( &$theme_json_structure, $domain = 'default' ) {
+		$preset_to_translate = self::get_presets_to_translate();
+		foreach ( $theme_json_structure as &$context_value ) {
+			if ( empty( $context_value ) ) {
+				continue;
+			}
+			foreach ( $preset_to_translate as $preset ) {
+				$path               = $preset['path'];
+				$translatable_keys  = $preset['translatable_keys'];
+				$array_to_translate = gutenberg_experimental_get( $context_value, $path, null );
+				if ( null === $array_to_translate ) {
+					continue;
+				}
+				foreach ( $array_to_translate as &$item_to_translate ) {
+					foreach ( $translatable_keys as $translatable_key ) {
+						if ( empty( $item_to_translate[ $translatable_key ] ) ) {
+							continue;
+						}
+						// phpcs:ignore WordPress.WP.I18n.LowLevelTranslationFunction,WordPress.WP.I18n.NonSingularStringLiteralText,WordPress.WP.I18n.NonSingularStringLiteralDomain
+						$item_to_translate[ $translatable_key ] = translate( $item_to_translate[ $translatable_key ], $domain );
+						// phpcs:enable
+					}
+				}
+				gutenberg_experimental_set( $context_value, $path, $array_to_translate );
+			}
+		}
+	}
+
 	/**
 	 * Return core's origin config.
 	 *
@@ -82,6 +161,7 @@ private static function get_core_origin() {
 		}
 
 		$config = self::get_from_file( __DIR__ . '/experimental-default-theme.json' );
+		self::translate_presets( $config );
 
 		// Start i18n logic to remove when JSON i18 strings are extracted.
 		$default_colors_i18n = array(
@@ -155,6 +235,7 @@ private static function get_core_origin() {
 	 */
 	private function get_theme_origin( $theme_support_data = array() ) {
 		$theme_json_data = self::get_from_file( locate_template( 'experimental-theme.json' ) );
+		self::translate_presets( $theme_json_data, wp_get_theme()->get( 'TextDomain' ) );
 
 		/*
 		 * We want the presets and settings declared in theme.json

lib/experimental-i18n-theme.json

@@ -0,0 +1,32 @@
+{
+	"settings": {
+		"typography": {
+			"fontSizes": [
+				"name"
+			],
+			"fontStyles": [
+				"name"
+			],
+			"fontWeights": [
+				"name"
+			],
+			"fontFamilies": [
+				"name"
+			],
+			"textTransforms": [
+				"name"
+			],
+			"textDecorations": [
+				"name"
+			]
+		},
+		"color": {
+			"palette": [
+				"name"
+			],
+			"gradients": [
+				"name"
+			]
+		}
+	}
+}