Our journey has involved a lot of thinking about language acquisition issues. The best-known and commercially successful theory for teaching languages during the past century believes that absolutely no English should ever be used, even if the learner is a complete beginner.

This approach forces the learner to connect words with pictures, while providing no guidance in the mother tongue. Not even on day one are there explanations in the learner's first language, since the belief is that adults should learn new languages in the same way they learned their first one as a young child.

But contemporary linguistics research suggests that adults learn languages differently than children. While children learn languages instinctively, as if they are hard-wired to acquire them, they lose this ability upon reaching puberty.

Around the age of 12 or 13, the brain essentially solidifies, radically changing how we learn languages. This is likely the reason it’s so difficult for adults—unlike children—to learn new languages without an accent. And it is the reason why adults shouldn’t expect to learn a new language in the same way they learned their mother tongue.

Those approaches that ban English from the teaching of a new language claim to take advantage of people’s natural language learning ability by trying to regress adults back to childhood. But since there is strong evidence that adults lose the innate language abilities they had as children, this no-English approach doesn’t make much sense.

The flip side is that adults have a major advantage over children when it comes to learning a new language: they already know an entire system of grammar and vocabulary—that of their own mother tongue. Because adults also have a highly developed sense of logic, they can learn new languages much more quickly by relating the grammar, syntax, and vocabulary of the language they already know to the one they are trying to learn.

Although adults can't learn new languages instinctively like children because their brains have changed, they can learn very quickly. The key is to use one’s knowledge of English as leverage for learning the new language.

If English and Mandarin share a similar way of creating the simple future, doesn't it make sense to draw this out? If the English words for "automobile" and "cell phone" share the same roots with several Romance languages, wouldn't it help to emphasize the association?

By approaching the new language from the point of view of English, what seems unintelligible is made clear. Seeing and understanding how something works is the first step to being able to use it yourself.