I am new to Alfresco and i'm in the process of "white labeling" it. So i created two files called invitation-service.properties and activities-service.properties in Alfresco\tomcat\shared\classes\alfresco\messages.
invitation-service.properties i put
# InviteSender messages
invitation.invitesender.email.subject=You have been invited to join the {1} site
activities-service.properties i put
# Activities (Activity Service / Feeds)
activities.feed.notifier.email.subject=Recent Activities
I restarted the Tomcat service, tested, but there were no changes. Am i missing something?