Add strings.

en.json

@@ -173,6 +173,15 @@
                     "cancel": "Cancel"
                 }
             },
+            "popovers": {
+                "user_profile": {
+                    "profile": "Profile",
+                    "mutual_friends": "Mutual Friends",
+                    "mutual_groups": "Mutual Groups",
+                    "no_users": "No mutual friends!",
+                    "no_groups": "No mutual groups!"
+                }
+            },
             "requires_online": "You need to be online to view this."
         },
         "context_menu": {