Few things you should know before going in:
Legacy products need a different approach than most modern tech stack applications
The automation framework has to deal with the various legacy platforms used
This means compatibility with those languages, platforms is essential
In some cases it can be advantageous too, e.g. front ends built with some JQuery or custom components might make things easier
The backend might not be as ‘automation friendly’ since it was never designed for anyone other than the developer to understand
Processes, tools and the team, all would come into play
More insights in this article:
https://goo.gl/B6kEX3
In situations like this you go and work with the developers of the legacy system to work on “baking in” Testability features and work towards Automatability of the target system. So just like you would work on testability for a new system/new technology you do the same for a legacy system. It will all be worth it, and does take minimal effort if planned properly.
Excellent suggestion Jim, it certainly makes things a lot easier if testability is added within the AUT. Thank you for adding.