In Site manager -> Development -> E-mail templates, you can find the following e-mail templates:
Friend approval - template for e-mail or message confirming that a user approved your friendship request
Friend rejection - template for e-mail or message confirming that a user rejected your friendship request
Friend request - template for e-mail or message notifying you about the fact that some user requested your friendship
If you choose to Edit (
) some of the templates, you will see two large text fields:
Text - text of the template used for e-mails
Plain text - text of the template used for messaging module messages