Move to smartling for translation services

ts/types/I18N.ts

@@ -1,21 +1,39 @@
 // Copyright 2020 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
+/* eslint-disable camelcase */
+
 import type { LocalizerType } from './Util';
 
-export type LocaleMessagesType = {
-  [key: string]: {
-    message: string;
-    description?: string;
-    placeholders?: {
-      [name: string]: {
-        content: string;
-        example: string;
-      };
+export type { LocalizerType } from './Util';
+
+type SmartlingConfigType = {
+  placeholder_format_custom: string;
+  translate_paths: Array<{
+    key: string;
+    path: string;
+    instruction: string;
+  }>;
+};
+
+type LocaleMessageType = {
+  message: string;
+  description?: string;
+  placeholders?: {
+    [name: string]: {
+      content: string;
+      example: string;
     };
   };
 };
 
+export type LocaleMessagesType = {
+  // In practice, 'smartling' is the only key which is a SmartlingConfigType, but
+  //  we get typescript error 2411 (incompatible type signatures) if we try to
+  //  special-case that key.
+  [key: string]: LocaleMessageType | SmartlingConfigType;
+};
+
 export type ReplacementValuesType<T> = {
   [key: string]: T;
 };