you should speak the language you are taught when you are a school child
What happens when parents speak one language and the schools teach in another? This isn't an issue unique to Wales, either; it exists in one form or another throughout the world. It is however, one of the most expensive issues in fiscal terms and the prime cause - along with religion - of torture, genocide, war, mass murder and child rape.
Language is a tool of thought. It's also the way in which humans communicate with each other and, given the capacity for misunderstanding which exists between them as it is, anything which might contribute to potential misunderstanding is obviously not desirable.
Colonisation of land by the major powers during the 15th - 19th centuries is largely responsible for the world's language distribution today. In the 1960s, prior to widespread television broadcasting, the international language was believed to be French, but this saw a gradual shift as trade between the previously xenophobic communist bloc countries and the West increased. Partly because the US has traditionally spearheaded both trade and colonisation through anti-communist adventuring, and partly because WWII was won by English-speaking countries (although Europeans might disagree), English supplanted French and is now acknowledged as the international language of Trade and diplomacy. The process was accelerated by the advent of satellite broadcasting. Astra footprints ensured that the Scandinavians could get Sky and - led by the linguists of Europe - the Dutch - the entire Northern Europe conglomerate became fluent in English. The ever-pragmatic Chinese, meanwhile, decided that their population, speaking 292 different languages between them, would be taught English as a common tongue, which left little choice for just about any other country other than to adopt English as their primary second language.
Today, mastery of English is essential for progression in any profession and the ubiquity of satellite broadcasting ensures that advertisers will not support minority languages. Even the great world languages such as Hindi are accepting this, and - particularly for
Dalits, whose status often eliminates opportunities to learn English - protection has been seen as necessary so their chances to live and work successfully in India will not be damaged.
The case of India and Pakistan is also interesting, in that it clearly shows the lethality of bigotry and mindless nationalism in separating what had been one homogeneous society into two, nuclear powers based solely on language and religion and it seems clear that the world will one day end through a conflagration sparked by little more than unreasoning hatred and bigotry for the language and beliefs of others. It's a sobering through that were an advanced civilisation from the stars able to visit us, they would almost certainly view us as in need of serious education and possible fumigation.