test(typings): Add langfile (msg) import + typings test

tests/typescript/src/msg.ts

@@ -0,0 +1,20 @@
+/**
+ * @license
+ * Copyright 2022 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * Test: Should be able to import messages and verify their type.
+ * Test at least one language other than English!
+ */
+
+import * as en from 'blockly-test/msg/en';
+import * as fr from 'blockly-test/msg/fr';
+
+let msg: {[key: string]: string};
+msg = fr;
+msg = en;
+
+// Satisfy eslint that msg is used.
+console.log(msg['DIALOG_OK']);