Joomla : Akeeba Subscriptions Emails

We've got a custom developed copy of Akeeba Subscriptions 2.2.1 running on Joomla 2.5. There's only a small number of subscription levels but some of those require the user to be sent to an external website to complete some additional information before returning back to our site where we get confirmation whether the transaction was successful or not. The issue we need to resolve is that a lot of the automated emails are not being sent out correctly, they are sending with the placeholder information eg. PLG_AKEEBASUBS_SUBSCRIPTIONEMAILS_HEAD_STANDARD_EXPIRED in the email body, instead of the information we've added into the language files. We're not 100% sure what all the combinations of emails there are, as it seems to have been customised from the Akeeba originals to accommodate some of the different subscription types that we've got. I don't think resolving this issue will be as simple as just ensuring that the correct wordings are in the correct language files, as these have been added previously but don't seem to be sending correctly. We have a list of which events we would like to trigger emails and have wording for each of the mails which we need to send. Our requirements are 1) To ensure that Akeeba Subs only sends out automated emails on the occasions we choose 2) To ensure that duplicate emails are not sent out for similar triggers such as Paid / Published / New Active 3) To setup and test that emails are being sent out with the correct content (provided by us) Previous experience of developing Akeeba Subscriptions is required for this project.