Im not fully sure if that spec can be changed but I starting from 11.20 SR8 are some of the messages configurable.
From the release notes:
Configurable Ajax Messages
Some of the messages sent in the AJAX client can now be configured to your own wording or translated
to another language.
You can change these messages in the file "customTranslations.js" supplied in the "Program
Files\QlikView\Server\QlikViewClients\QlikViewAjax\htc\customFiles" folder on the machine where
the QV WebServer runs.
A file named customTranslationsExample.js is also provided that shows syntax and which messages that
can be configured.