This advice, as one minority language commentator notes here, is usually proffered by those who can’t speak any of these languages themselves.
However, it’s a point worth considering. In 2014 China became the largest economy on earth. Wouldn’t every child in Wales benefit from a Chinese education?
Of course they would, just as learning any other language could be beneficial. And if they plan on moving to China, or interacting with Mandarin speakers from day to day, it’s certainly recommended.
An education can only take you so far towards fluent bilingualism, however. A Chinese education would not be of use for the vast majority of pupils in Wales, who, as things stand, would have little opportunity to use it outside the school.
Welsh, in the meantime, is a living language in Wales, spoken by one in five of the population. If one desired to do so one could live the majority of their life through the medium of Welsh, as many do.
In Wales, at least, Welsh remains a more ‘useful’ language, in terms of the financial and cultural opportunities it offers the speaker, than any other bar English.