I believe the current default Translation Summary by Language Report available under Management Reports in SDL TMS is ineffective.
From experience, when trying to use this to collate data for customer KPIs and business reviews, it seems that this report shows throughput rather than translated volumes.
In the past, I've had custom reports deployed on a number of implementations (JLR for instance) with a customized report that will only include jobs that have been through an authorization stage and ended up in translation - this is much more accurate and avoids the inclusion of any terminated jobs, or jobs that were uploaded in error or for analysis only.
This enables us to demonstrate realistic metrics, TM savings etc to clients, rather than the data being inflated by jobs that shouldn't be included.
In my opinion, this should be added as a default report option to the core product, as it is much more useful than the current report which a lot of project managers may be using in error.