Theme i18n: Add a block to allow strings in template files to be translated

lib/blocks.php

@@ -27,6 +27,7 @@ function gutenberg_reregister_core_block_types() {
 				'heading',
 				'html',
 				'home-link',
+				'i18n',
 				'image',
 				'list',
 				'media-text',
@@ -60,6 +61,7 @@ function gutenberg_reregister_core_block_types() {
 				'navigation.php'                => 'core/navigation',
 				'navigation-link.php'           => 'core/navigation-link',
 				'home-link.php'                 => 'core/home-link',
+				'i18n.php'                      => 'core/i18n',
 				'rss.php'                       => 'core/rss',
 				'search.php'                    => 'core/search',
 				'shortcode.php'                 => 'core/shortcode',

packages/block-library/src/i18n/block.json

@@ -0,0 +1,16 @@
+{
+	"apiVersion": 2,
+	"name": "core/i18n",
+	"title": "i18n",
+	"category": "text",
+	"description": "Pass strings to PHP for i18n.",
+	"supports": {
+		"html": false
+	},
+	"textdomain": "default",
+	"attributes": {
+		"text": {
+			"type": "string"
+		}
+	}
+}

packages/block-library/src/i18n/index.js

@@ -0,0 +1,16 @@
+/**
+ * WordPress dependencies
+ */
+
+/**
+ * Internal dependencies
+ */
+import metadata from './block.json';
+
+const { name } = metadata;
+export { metadata, name };
+
+export const settings = {
+	edit: () => {},
+	save: () => {},
+};

packages/block-library/src/i18n/index.php

@@ -0,0 +1,30 @@
+<?php
+
+$i18n_strings_file = get_stylesheet_directory() . '/i18n.php';
+if ( file_exists ( $i18n_strings_file ) ) {
+	require_once $i18n_strings_file;
+}
+
+/**
+ * Registers the block using the metadata loaded from the `block.json` file.
+ *
+ * @see https://developer.wordpress.org/block-editor/tutorials/block-tutorial/writing-your-first-block-type/
+ */
+function register_block_core_i18n() {
+	register_block_type_from_metadata(
+		__DIR__ . '/i18n',
+		array(
+			'render_callback' => 'render_block_i18n',
+		)
+	);
+}
+
+function render_block_i18n( $attributes ) {
+	if ( defined( 'i18n' ) && ! empty ( i18n[ $attributes['text'] ] ) ) {
+		return i18n[ $attributes['text'] ];
+	};
+
+	return $attributes['text'];
+}
+
+add_action( 'init', 'register_block_core_i18n' );