Duh, we need this file.

Foreground.i18n.php

@@ -0,0 +1,35 @@
+<?php
+/**
+ * This is a backwards-compatibility shim, generated by:
+ * https://git.wikimedia.org/blob/mediawiki%2Fcore.git/HEAD/maintenance%2FgenerateJsonI18n.php
+ *
+ * Beginning with MediaWiki 1.23, translation strings are stored in json files,
+ * and the EXTENSION.i18n.php file only exists to provide compatibility with
+ * older releases of MediaWiki. For more information about this migration, see:
+ * https://www.mediawiki.org/wiki/Requests_for_comment/Localisation_format
+ *
+ * This shim maintains compatibility back to MediaWiki 1.17.
+ */
+$messages = array();
+if ( !function_exists( 'wfJsonI18nSkinForeground' ) ) {
+	function wfJsonI18nSkinForeground( $cache, $code, &$cachedData ) {
+		$codeSequence = array_merge( array( $code ), $cachedData['fallbackSequence'] );
+		foreach ( $codeSequence as $csCode ) {
+			$fileName = dirname( __FILE__ ) . "/i18n/$csCode.json";
+			if ( is_readable( $fileName ) ) {
+				$data = FormatJson::decode( file_get_contents( $fileName ), true );
+				foreach ( array_keys( $data ) as $key ) {
+					if ( $key === '' || $key[0] === '@' ) {
+						unset( $data[$key] );
+					}
+				}
+				$cachedData['messages'] = array_merge( $data, $cachedData['messages'] );
+			}
+
+			$cachedData['deps'][] = new FileDependency( $fileName );
+		}
+		return true;
+	}
+
+	$GLOBALS['wgHooks']['LocalisationCacheRecache'][] = 'wfJsonI18nSkinForeground';
+}