Adds support for localized push notification in push payload (#4129)

* Adds support for localized push data keys

- passign alert-[lang|locale] or title-[lang|locale] will inject the
  proper locale on the push body based on the installation

* Better handling of the default cases

* Updates changelog

* nits

* nits

src/Push/PushWorker.js

@@ -65,6 +65,22 @@ export class PushWorker {
 
   sendToAdapter(body: any, installations: any[], pushStatus: any, config: Config): Promise<*> {
     pushStatus = pushStatusHandler(config, pushStatus.objectId);
+    // Check if we have locales in the push body
+    const locales = utils.getLocalesFromPush(body);
+    if (locales.length > 0) {
+      // Get all tranformed bodies for each locale
+      const bodiesPerLocales = utils.bodiesPerLocales(body, locales);
+
+      // Group installations on the specified locales (en, fr, default etc...)
+      const grouppedInstallations = utils.groupByLocaleIdentifier(installations, locales);
+      const promises = Object.keys(grouppedInstallations).map((locale) => {
+        const installations = grouppedInstallations[locale];
+        const body = bodiesPerLocales[locale];
+        return this.sendToAdapter(body, installations, pushStatus, config);
+      });
+      return Promise.all(promises);
+    }
+
     if (!utils.isPushIncrementing(body)) {
       return this.adapter.send(body, installations, pushStatus.objectId).then((results) => {
         return pushStatus.trackSent(results);