Add remaining translations!

Every file has now been manually vetted by me. Due to the extent of
the changes, I've been unable to test all scenarios to make sure this
all works. :(

src/components/views/rooms/SimpleRoomHeader.js

@@ -20,6 +20,7 @@ import React from 'react';
 import dis from '../../../dispatcher';
 import AccessibleButton from '../elements/AccessibleButton';
 import sdk from '../../../index';
+import { _t } from '../../../languageHandler';
 
 // cancel button which is shared between room header and simple room header
 export function CancelButton(props) {
@@ -28,7 +29,7 @@ export function CancelButton(props) {
     return (
         <AccessibleButton className='mx_RoomHeader_cancelButton' onClick={onClick}>
             <img src="img/cancel.svg" className='mx_filterFlipColor'
-                width="18" height="18" alt="Cancel"/>
+                width="18" height="18" alt={_t("Cancel")}/>
         </AccessibleButton>
     );
 }