If you try to add another answer to a question you have already answered you get the following pop up:
Are you sure you want to add another answer?
You could use the edit link to refine and improve your existing answer, instead.
which shows that the whole spirit of Stack Exchange sites is to work together
to build a library of detailed answers to every question about the French language.
I personally cannot see the point of adding another answer, what would you gain ? More answer points (I do not think most people come here in order to get points but in order to learn & exchange). What would the site get? Unorganized answers and messy pages.
There is no risk of additions being unnoticed because as soon as the slightest edit is made to a question or to an answer it is brought to the top of the home page. And if you worry about the person who asked the question not noticing it, then you can always ping them through a comment. Keeping in mind that some people ask questions but do not always bother to come back and see the answers, for those a new answer or an edit won't change a thing.
Some people specify that they are making an edit to add something to their answers.