[[MediaWiki:Mwe-upload-once-done/en]]

It seems highly likely that $1 and $2 are the two messages after it:

• Mwe-upload-in-new-win-link ("upload in the new window or tab")
• Mwe-upload-refresh ("refresh your upload list")

I have e-mailed Michael Dale about this. You might want to bugzilla: this, too.