diff --git a/Gruntfile.js b/Gruntfile.js
index 2a6d2b9fbaa5..a9ab00cb0576 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -1462,6 +1462,17 @@ module.exports = function(grunt) {
 		);
 	} );
 
+	grunt.registerTask( 'copy:theme-json', 'Copies theme.json file contents to theme-json.php.', function() {
+		[ 'theme.json', 'theme-i18n.json' ].forEach( function( fileName ) {
+			var themeData = grunt.file.readJSON(SOURCE_DIR + 'wp-includes/' + fileName);
+			var newFileName = fileName.replace('.', '-');
+			grunt.file.write(
+				SOURCE_DIR + 'wp-includes/assets/'+ newFileName + '.php',
+				'<?php return ' + json2php(themeData) + ';'
+			);
+		});
+	} );
+
 	grunt.registerTask( 'copy:js', [
 		'copy:npm-packages',
 		'copy:vendor-js',
@@ -1511,6 +1522,7 @@ module.exports = function(grunt) {
 		'clean:files',
 		'copy:files',
 		'copy:block-json',
+		'copy:theme-json',
 		'copy:version',
 	] );
 
@@ -1650,6 +1662,7 @@ module.exports = function(grunt) {
 			grunt.task.run( [
 				'build:js',
 				'build:css',
+				'copy:theme-json',
 			] );
 		} else {
 			grunt.task.run( [
diff --git a/src/wp-includes/class-wp-theme-json-resolver.php b/src/wp-includes/class-wp-theme-json-resolver.php
index 14c8208f0182..b6c3c2ad773e 100644
--- a/src/wp-includes/class-wp-theme-json-resolver.php
+++ b/src/wp-includes/class-wp-theme-json-resolver.php
@@ -143,7 +143,14 @@ public static function get_fields_to_translate() {
 	 */
 	protected static function translate( $theme_json, $domain = 'default' ) {
 		if ( null === static::$i18n_schema ) {
-			$i18n_schema         = wp_json_file_decode( __DIR__ . '/theme-i18n.json' );
+			$file_path = __DIR__ . '/assets/theme-i18n-json.php';
+			if ( file_exists( $file_path ) ) {
+				$i18n_schema = require $file_path;
+				$i18n_schema = json_decode( json_encode( $i18n_schema ) );
+			} else {
+				$i18n_schema = wp_json_file_decode( __DIR__ . '/theme-i18n.json' );
+			}
+
 			static::$i18n_schema = null === $i18n_schema ? array() : $i18n_schema;
 		}
 
@@ -162,7 +169,13 @@ public static function get_core_data() {
 			return static::$core;
 		}
 
-		$config = static::read_json_file( __DIR__ . '/theme.json' );
+		$file_path = __DIR__ . '/assets/theme-json.php';
+		if ( file_exists( $file_path ) ) {
+			$config = require $file_path;
+		} else {
+			$config = static::read_json_file( __DIR__ . '/theme.json' );
+		}
+
 		$config = static::translate( $config );
 
 		/**