Can i replace Ms-Dos with Java or Python?

My uncle has a Pharmacy and his store has a Ms-Dos program for making bills, which he pays a Programmer each month to come and fix it(more like paying a monthly subscription to the guy). So i saw the program and i was like can i not program for him another application like this but with Java or Python. I have no knowledge on Ms-Dos, but i do know Java and Python, so i think that Java or Python would do more better in designs and user-interface than boring Ms-Dos blue program(seriously the blue background is boring). I got this idea from supermarkets, they have very good designed billing programs and easy accessable. So, to design him a program, must i learn Ms-Dos or use Java/Python? Please give me any idea.