If you get the "Missing lang: error forgot password" message, it means that you have not set correctly the email account that sends out notifications or there has been an error with it, and you will not be receiving the lost password email.
In order to retrieve your password, I suggest you to look for the queued_mails table in the data base, look for the email which was supposed to be sent to your email address to retrieve your password, and use the link provided there to change your password.
PS: We will be correcting that missing lang for a future version
Best regards,
Francisco