Do not underestimate the urge to procrastinate (by still doing productive things, like learning Mandarin) while pursuing a PhD.

I am not sure if this will be the author's experience too, but pursuing a PhD will often leave you exhausted without any hope of ever finding "the final missing ingredient" to solve the problem you are currently tackling. So turning to entirely unrelated problems, however productive they may seem to outsides, suddenly becomes an attractive alternative in order to procrastinate.