I had two questions asking how to change the Out of Office Subject field. The subject of the initial message, usually Autoreply: [subject], can't be changed, you can send a more informative automatic reply to some users using Autoreply rules (they'll get the default autoreply and the custom message).
The first question:
We have Exchange 2010 installed on a French Windows server and the subject field on the Out of Office messages are in French. How do we set it to English?
You can change the subject line (and more) by running the Set-Mailbox cmdlet:
Set-Mailbox -Identity "mailbox name" -Languages en-US
See Set-Mailbox for more information on the parameters available in the Set-Mailbox cmdlet.
Out of Office (Automatic Reply) Rules
The second question was from a user who wanted to customize the subject on the Out of Office messages she sends.
To change the subject used for the automatic reply messages, you need to set up an Out of Office reply rule that uses a template.
Open the Automatic replies dialog and click Rules (in the lower left).
Click Add Rule.
Then enable Reply with and click Template.
Add the subject and message body to the template then click Save and Close.
If you want to restrict the message to certain senders, messages with specific subjects, or other conditions, enter this information at the top of the Edit Rule dialog. Leaving the condition fields blank will apply the rule to all messages received.