This is a great question and we can think about it in two ways depending on why you want to teach a language.
The first and most exciting reason for teaching a language is because of the wide-ranging cognitive, social and linguistic benefits. Teaching a language, especially to a young child, creates life-long benefits such as improved memory; faster decision making; enhanced divergent thinking; increased creativity; a love of learning; greater understanding of their own mother tongue; improved performance across the board in academic and creative pursuits; markedly improved proficiency in learning additional languages; improved communication skills; improved social skills; greater confidence; and a broader world view and cultural acceptance. Phew!
If these are the outcomes you are looking for, then theoretically it doesn’t matter which language you choose as every language will deliver these incredible benefits. Take your pick from Arabic or Zulu or even Latin.
But practically speaking, there are a few factors to consider in choosing the right language for you so that we can get the best outcomes. Remember, the goal is to develop a genuine proficiency in the language so that the child becomes at least conversationally fluent, or ideally, native-like. To do this, we need to create an environment where the language student is surrounded with opportunities to absorb and practice the language, as frequently as possible. So on this basis, think about these factors:
a) Family connection – does someone in the family already speak another language?
b) Ease of support – which languages will the parents and carers be best able to support?
c) Personal interest – does the child have an interest in another language already?
d) Resources – what resources will you be able to access?
e) Travel – are there countries that you may travel to where the language will be relevant?
f) School – does your future school have a language program?
Of all of the above factors, the most important to me is that of ‘ease of support’. Just like when they are learning English, a child will need support from the adults around them to learn a foreign language. This might mean playing games, reading books, listening to music, practicing pronunciation etc. And basically, the easier the adults find the language, the more support they will be able to offer.
For me, Spanish wins this competition hands-down: there are 5000 words that are similar between English and Spanish; it is a phonetic language; it uses the same alphabet and perfect pronunciation isn’t crucial. For these reasons, Spanish is particularly easy to learn for English speakers. But compare this to Mandarin: I’m not sure there are any words similar between English and Mandarin; it is not phonetic; it uses different symbols; and it is tonal (which means that the pronunciation of a word changes its meaning). In my book, Mandarin would be a challenging choice because it is harder for the adults around the child to support them.
Now on to the other reason for teaching a language: because you want them to be proficient in that specific language. That is, the proficiency of a specific language is your primary goal, and the cognitive, social and linguistic benefits are secondary. In this case, you are probably thinking about which language will give children the greatest career, travel and lifestyle benefits.
What’s important to think about here is which languages will be most dominant and relevant when your children are launching themselves in to the global village. If your child is 5 years old now, which languages will be important when they are 20 or 25 years old, therefore in 15 or 20 years’ time?
If you see a future for your children working in China or doing business with Chinese companies, then a Chinese language like Mandarin might be the right language. Similarly, we are also seeing a huge rise in the power of India in business and commerce, so perhaps an Indian language like Hindi would suit. Or if you see a diplomatic future for your child, perhaps Arabic might be a good choice, or French which continues to be a global diplomatic language. Or perhaps you see a future in aid and humanitarian or environment service such as in Africa, in which case an African language would help. Hopefully what you see from these examples is that there is no clear one-language-fits-all. It depends on what specifically you have in mind.
In the absence of a specific need, again, my vote goes to Spanish. Spanish is the second most commonly spoken language in the world and the fast growing. And extremely globally diverse, from South America, to Central America, to North America to Europe. In fact, some statistics predict that by 2025, the United States of America will be a Spanish-speaking country. Wow.
So, unless you have something specific in mind and a reason for choosing a specific language, my vote goes to Spanish as the ‘best’ general language to open as many doors as possible and create a lifetime of opportunity.