Is 14/20 a good grade on master studies in France?
Your question is a bit too broad; even restricting to classes I graded or saw graded by others, the answer can vary a lot. What I can say with some confidence (after about 20 years as a student then teacher in French higher education in mathematics) is:


it is almost universal (by law!) that the passing grade is 10, so all grades above 10 should mean the work deserves more than just a passing grade,
in some classes (projects, internships, etc.) 14 might be a bit plain, but still good,
in most written exam classes at the licence level (first to third year), 14 is pretty good but not outstanding,
in most written exam classes at the masters level (fourth and fifth year), 14 is between pretty good to very good (the best grade in a course can be lower than that).


Of course, on some occasion I have been disappointed by a 14. But in higher education I don't think I ever thought it was disgraceful. 

To make a comparison I have seen quite a few files from Italians, our grading system is very different. Every Italian application I ever saw but one had maximal grades everywhere (70/70 or 110/110), while that is very rare in France for a single grade, let alone an yearly average.