It depends what your goals are and where you want to live. For instance, if you want to teach in Montessori preschools or Waldorf/Rudolf Steiner preschools, there are training programs specific to those teaching methods. Some of them can be done while working (for instance, there are summer programs that let you gain Montessori credentials while you spend the school year working in a preschool).
As for where you want to live, what citizenship(s) do you have? Are you dual US/EU? That would expand your options massively. If you are just a US citizen, I would suggest researching what French-immersion preschools exist in the US. You could also research what French magnet schools there are (many cities have public school "magnet" programs where one particular public school is dedicated to teaching one or more languages along with the usual curriculum; some of the magnet programs include French).
When you know what types of schools offer French immersion, you will have a better idea of what educational path to pursue to get there. For instance, if you see several French-immersion Montessori preschools in places you wouldn't mind living, that might point you toward getting training in the Montessori method. If you end up leaning toward Montessori, Waldorf, or public school teaching certification, then come back to this board (or even this thread) and ask for advice on the best way to get that type of training.
Last updated Dec 01 '17 at 12:44