How to translate between programming languages

I am setting out to do a side project that has the goal of translating code from one programming language to another. The languages I am starting with are PHP and Python (Python to PHP should be easier to start with), but ideally I would be able to add other languages with (relative) ease. The plan is:

Compiling an AST back to source code

I'm currently in the process of building a PHP Parser written in PHP, as no existing parser came up in my previous question . The parser itself works fairly well.