The thing is, Japan gets TCG cards first, but because English is basically the official international language of the TCG (and they go by English sets for determining a card's Worlds legality), every card does get released in English at some point. It's just a matter of The Pokemon Company International deciding on which cards printed in Japan to translate for their next set, actually translating them, and then getting enough print runs built up in anticipation of the rush of sales of the set when it debuts.
One key thing to note is that TPCi does not handle the Japanese printings of cards. The company in charge of the Japanese releases is Media Factory.