i18n group updates (#1549)

// FREEBIE

_locales/en/messages.json

@@ -847,5 +847,39 @@
     },
     "autoUpdateLaterButtonLabel": {
       "message": "Later"
+    },
+    "leftTheGroup": {
+      "message": "$name$ left the group.",
+      "description": "Shown in the conversation history when someone leaves the group",
+      "placeholders": {
+        "name": {
+          "content": "$1",
+          "example": "Bob"
+        }
+      }
+    },
+    "updatedTheGroup": {
+      "message": "Updated the group.",
+      "description": "Shown in the conversation history when someone updates the group"
+    },
+    "titleIsNow": {
+      "message": "Title is now '$name$'.",
+      "description": "Shown in the conversation history when someone changes the title of the group",
+      "placeholders": {
+        "name": {
+          "content": "$1",
+          "example": "Book Club"
+        }
+      }
+    },
+    "joinedTheGroup": {
+      "message": "$names$ joined the group.",
+      "description": "Shown in the conversation history when people join the group",
+      "placeholders": {
+        "names": {
+          "content": "$1",
+          "example": "Alice, Bob"
+        }
+      }
     }
 }

js/models/messages.js

@@ -76,15 +76,15 @@
             if (this.isGroupUpdate()) {
                 var group_update = this.get('group_update');
                 if (group_update.left) {
-                    return group_update.left + ' left the group.';
+                    return i18n('leftTheGroup', group_update.left);
                 }
 
-                var messages = ['Updated the group.'];
+                var messages = [i18n('updatedTheGroup')];
                 if (group_update.name) {
-                    messages.push("Title is now '" + group_update.name + "'.");
+                    messages.push(i18n('titleIsNow', group_update.name));
                 }
                 if (group_update.joined) {
-                    messages.push(group_update.joined.join(', ') + ' joined the group.');
+                    messages.push(i18n('joinedTheGroup', group_update.joined.join(', ')));
                 }
 
                 return messages.join(' ');