Fix locales again (#3010)

* Normalize locales

* Restore "mention" locale key

app/javascript/mastodon/actions/notifications.js

@@ -2,6 +2,7 @@ import api, { getLinks } from '../api'
 import Immutable from 'immutable';
 import IntlMessageFormat from 'intl-messageformat';
 import { fetchRelationships } from './accounts';
+import { defineMessages } from 'react-intl';
 
 export const NOTIFICATIONS_UPDATE = 'NOTIFICATIONS_UPDATE';
 
@@ -16,6 +17,10 @@ export const NOTIFICATIONS_EXPAND_FAIL    = 'NOTIFICATIONS_EXPAND_FAIL';
 export const NOTIFICATIONS_CLEAR      = 'NOTIFICATIONS_CLEAR';
 export const NOTIFICATIONS_SCROLL_TOP = 'NOTIFICATIONS_SCROLL_TOP';
 
+const messages = defineMessages({
+  mention: { id: 'notification.mention', defaultMessage: '{name} mentioned you' },
+});
+
 const fetchRelatedRelationships = (dispatch, notifications) => {
   const accountIds = notifications.filter(item => item.type === 'follow').map(item => item.account.id);