In addition that you will need to find and negotiate the use of some markup, will need to train Directors in the use of this language. This second task can be much more unmanageable than first.
With regard to languages for describing/modeling and reporting forms, the well-known standards. Everything is always bound to a specific BI tool and built into its graphical IDE with which these reports are: MS SSRS
, Crystal Reports, Cogons BI, Oracle BI, etc.
In simple cases it would be possible to do the usual UML with the addition of OCL, but do you will that be enough?
If you try to solve another problem - to see the changes in the TOR of the reporting form, you do not need a language, a tool for managing requirements (or ALM system).