When should a child learn a second language?

I agree with experts answer. Thanks for the invitation

I think it depends on the mother, I taught my kids a second language when they were only 6 months old, not that they could speak it but they do understand it properly. 

I think the best time for Today's Generation is 5 or 6 because under these age they are not in educational age they should be free and playing , they learn alot by nature not education.

Thanks for your invitation. The world has changed enough and future will by multilingual only. It will be mandatory for the new generation to adopt some other international languages too to boost up their career and identity of experience. Children are usually sharp, intelligent and easy learner. I recomend to learn them other languages especially, English, French, Mandrin and Arabic. 

As early as possible - kids are very flexible 

10years is the age for learning a second language

I agree with Samah answer Thanks

i think in  the primary school

Thanks for your invitation

I think it's better to lerned the second language after they awareness the native or main language otherwise interferance happened, 5-7 age, at this age they began to mix with other child or social.

A child should start being exposed through reading materials, cartoons, movies, learning games and so forth to a second language right from the moment they start communicating verbally using comprehensive words. Toddlers are at the prime of their learning and retention ability compared to teenagers and adults. As from the age of 3 or 4, they have this amazing ability of learning and retaining whatever is taught to them. Moreover, as they learn their own language and its words, linking the words in one language to the ones in the second language and their meanings makes it easier for a child to understand the varying meanings and where and how to use them in both languages. The proof is very visible in my country where all children are exposed to at least four different languages right from the age of 3yrs old in schools. All of our citizens are multilinguals.