Yes, it
can convert them, but I guess what you meant was "Is Penelope taking into account the .syn file inside a StarDict dictionary?", to which the answer is no.
I acknowledge this could be a nice feature, but I have never come across to one such dictionary (
legally available for free). Do you have a link?
BTW, the code of Penelope is on GitHub under the terms of the MIT license (
https://github.com/pettarin/penelope ): unfortunately I do not have time to work on it, but anyone willing to implement new features, write documentation, etc. is welcome to join the project.