My question is concerned with the idea of putting on your resume that you know a official language but have mostly experimented with its open-source counterpart (Example: putting down you know MATLAB but you know Octave which is almost similar to MATLAB). Also I plan to learn other languages like Mathematica and IDL and SPSS but I have found their open source free counterparts and I have been wondering if I can practice with the open-source software and then put down on my resume that I know the "offical" programming language.
Any feedback would be much appreciated.