diff --git a/locales/en.json b/locales/en.json
index 187596dd5..e6bef7aba 100644
--- a/locales/en.json
+++ b/locales/en.json
@@ -19,12 +19,12 @@
     "app_no_upgrade" : "No app to upgrade",
     "app_not_installed" : "{app:s} is not installed",
     "app_not_correctly_installed" : "{app:s} seems to be not correctly installed",
-    "custom_app_url_required" : "You must provide an URL to upgrade your custom app {:s}",
+    "custom_app_url_required" : "You must provide an URL to upgrade your custom app {app:s}",
     "app_recent_version_required" : "{app:s} requires a more recent version of YunoHost",
     "app_upgraded" : "{app:s} successfully upgraded",
     "app_upgrade_failed" : "Unable to upgrade {app:s}",
     "app_id_invalid" : "Invalid app id",
-    "app_already_installed" : "{:s} is already installed",
+    "app_already_installed" : "{app:s} is already installed",
     "app_removed" : "{app:s} successfully removed",
     "app_location_already_used" : "An app is already installed on this location",
     "app_location_install_failed" : "Unable to install the app on this location",
@@ -75,8 +75,8 @@
     "dyndns_cron_remove_failed" : "Unable to remove DynDNS cron job",
     "dyndns_cron_removed" : "DynDNS cron job successfully removed",
 
-    "port_available" : "Port {} is available",
-    "port_unavailable" : "Port {} is not available",
+    "port_available" : "Port {port:d} is available",
+    "port_unavailable" : "Port {port:d} is not available",
     "port_already_opened" : "Port {} is already opened for {:s} connections",
     "port_already_closed" : "Port {} is already closed for {:s} connections",
     "iptables_unavailable" : "You cannot play with iptables here. You are either in a container or your kernel does not support it.",
diff --git a/src/yunohost/app.py b/src/yunohost/app.py
index 791c899a7..b88006a13 100644
--- a/src/yunohost/app.py
+++ b/src/yunohost/app.py
@@ -343,7 +343,7 @@ def app_upgrade(auth, app=[], url=None, file=None):
         elif url:
             manifest = _fetch_app_from_git(url)
         elif new_app_dict is None or 'lastUpdate' not in new_app_dict or 'git' not in new_app_dict:
-            logger.warning(m18n.n('custom_app_url_required', app_id))
+            logger.warning(m18n.n('custom_app_url_required', app=app_id))
             continue
         elif (new_app_dict['lastUpdate'] > current_app_dict['lastUpdate']) \
               or ('update_time' not in current_app_dict['settings'] \
@@ -458,7 +458,7 @@ def app_install(auth, app, label=None, args=None):
     if instance_number > 1 :
         if 'multi_instance' not in manifest or not is_true(manifest['multi_instance']):
             raise MoulinetteError(errno.EEXIST,
-                                  m18n.n('app_already_installed', app_id))
+                                  m18n.n('app_already_installed', app=app_id))
 
         # Change app_id to the forked app id
         app_id = app_id + '__' + str(instance_number)
@@ -813,10 +813,10 @@ def app_checkport(port):
         s.connect(("localhost", int(port)))
         s.close()
     except socket.error:
-        logger.success(m18n.n('port_available', int(port)))
+        logger.success(m18n.n('port_available', port=int(port)))
     else:
         raise MoulinetteError(errno.EINVAL,
-                              m18n.n('port_unavailable', int(port)))
+                              m18n.n('port_unavailable', port=int(port)))
 
 
 def app_checkurl(auth, url, app=None):
@@ -1014,7 +1014,7 @@ def _get_app_settings(app_id):
             return settings
     except (IOError, TypeError, KeyError):
         logger.exception(m18n.n('app_not_correctly_installed',
-                app=app_id))
+                                app=app_id))
     return {}