Why teach/learn a foreign language?
Learning and teaching a foreign language involves exploration of knowledge and skills resulting in an enrichment of the self at several levels, cognitive, cultural and interpersonal. This process is essential to better apprehend and live in the complexity of the modern world; it simply is worth it.
Pourquoi apprendre une langue étrangère?

a) 25 reasons to learn a foreign language by Renate Latimer, Professor Emeritus at Auburn University department of Foreign Languages and Literatures (OR we would rename the article “24 very good and 1 essential reasons to study and master Foreign Languages”)
b) Treating Language as a Strength. The Benefits of Bilingualism by Theresa Deussen in Northwest Matters
c) Why learn another language.Middlebury Interactive Languages
d) 5 Reasons why everyone should know at least two languages. Middlebury Interactive Languages

But why French?
French is definitely worth it! Why invest in mastering it in just 5 reasons.
Mais pourquoi le français?

5 reasons to invest in French from http://www.diplomatie.gouv.fr/en/french-foreign-policy/francophony/promoting-french-around-the-world-7721/article/10-good-reasons-for-learning