You've just said it. It takes a few years to acquire the necessary level in local language to access the academic stream, And same, albeit lower level, for second national language- even if the child is keen, motivated and academically very able. If you have an academic child, the last thing you want is for said child to find themselves in vocational stream - for all sorts of reasons. There are possibilities to switch over to the academic stream at a later stage, but it is NOT easy and requires a lot of dedication and support.