A: I’m thinking of taking up French.

B: Go for it! It’s always good to add another string to your bow.

Note: If you have another string to your bow, you have an extra skill that you can use if you do not succeed using your main skill. A second string means simply “an alternative resource or course of action.” This is a metaphor from archery. Since bowstrings are the most easily replaced part of a bow, archers often carry several of them, to make sure that at least one will work at maximum efficiency.