Hi,
I have TDL databases where the "Due date" is really the date it has to be finished, i.e. it is not an expectation as suggested if you add "prévisonnelle".
So, to keep the TDL tool open for multi-usages, I recommand to keep the current French translation unchanged: it is a simple neutral translation of "Due Date".
In my opinion: if you start introducing additional "flavours" in non-English title translations, it will break the consistency / understanding / interpretation of the application (fields / titles) across languages.
As solution to fine tune your database, you might add an additional field (i.e. coloumn) of type 'date' and labelled 'Date de fin prévisionnelle'.
This way, you would be able to catch, sort and filter this information (and this, in addition of the real 'due date' when / if applicable).
Regards - Eric