Steps to replicate the issue (include links if applicable):

• Go to the EnWiki ArbCom block appeal form (implemented in EnWikiContactPages.php)
• Fill out and submit the form (please indicate that it's a test, and test sparingly, if done on the live wiki)
• Submit the form

What happens?:
The emailsenttext message defined in core states that the username of the recipient will be passed to the message, but when ContactPage displays the emailsenttext message, it does not pass the recipient username. On Wikis which use the parameter in their custom messages, this leads to differences in behavior between Special:EmailUser and Special:Contact. Example from EnWikit:

Your email message has been sent. $1 will also receive a notification about your email unless they have disabled this in their preferences.
You can additionally notify users that you have emailed them by leaving them a talk page message. The {{You've got mail}} template is available for this purpose. Click new section to use it on User talk:$1.

What should have happened instead?:
The variable should reference User:Arbitration Committee who is the specified user and whose email address successfully receives the email.

Your email message has been sent. Arbitration Committee will also receive a notification about your email unless they have disabled this in their preferences.
You can additionally notify users that you have emailed them by leaving them a talk page message. The {{You've got mail}} template is available for this purpose. Click new section to use it on User talk:Arbitration Committee.

It would also be nice if we could customize this message as well, but that's probably out of scope for this task.