Thread:Support/MediaWiki:Wikieditor-toolbar-dialogs-preference/en/reply

Altered messages need to be deployed into the distributed software files. This is not possible for English as a matter of workflow:
 * 1) Programmers create english messages while they are updating programs in the software repository.
 * 2) The English messages get copied from there and are kept here at twn.
 * 3) Translators read English messages, and translate them.
 * 4) Translations get copied from twn back to the software repository.

Both copy operations are unidirectional so as to not run into problems with duplicate or inconsistent parallel changes.

Think over it, it makes sense as it is set up.

You can alter English messages. Either do it in the source code if yo've got access rights, or file a bug asking developers to do it.