[ci skip] Add setLocale, fixes #4091

Author: MGatner

user_guide_src/source/outgoing/localization.rst

@@ -52,6 +52,8 @@ method that will automatically perform :doc:`content negotiation </incoming/cont
 determine the correct locale to use. The second method allows you to specify a segment in your routes that
 will be used to set the locale.
 
+Should you ever need to set the locale directly you may use ``IncomingRequest::setLocale(string $locale)``.
+
 Content Negotiation
 -------------------