If the user set the welcome msg, don't add anything to it

Was adding a default message over the user's message if the meeting was being
recorded. If the user set a message, he can decide if he wants to warn the
user that the session is being recorded or not.
And allows it to be done in other languages.
Add localization support, with en and pt_BR for now

Only the strings shown to the end user are localized, the strings in the
management pages are still only in English.