Does the choice of programming language affect paper acceptance in mechanical engineering? I have published papers in the field of mechanical engineering, combustion, engines, etc. Previously I relied on MATLAB for most of my data processing, and C++/Fortran for computations. I duly cite languages used.

Recently I switched to Python for its great comprehensive library, plotting capabilities, support and above all I don't have to struggle with the licensing issues. Now I am worried if citing Python would affect paper acceptance, since it is based on an unconventional approach.

Will using an unconventional programming language increase my chances of rejection?
The short answer is, no.  I've never experienced or heard of a reviewer caring about what language was used for code in a science or engineering paper.

In any case, I don't think Python is "unconventional" in 2015.  Here are some well-known and widely used codes that can be used for CFD with Python front-ends:


http://pyfr.org 
http://fenicsproject.org
http://github.com/clawpack/pyclaw


Note that all of these use Python in combination with lower-level languages for performance.

I'll also mention the educational course CFD Python.