Edit: Sorry, missed this important little tid-bit: You can only use foreign-language cards from Supreme Victors and earlier. So, don’t buy any foreign cards in the future as the second paragraph was saying. POP is definitely phasing out their use.
Mike Liesik, one of the heads of Pokemon Organized Play, has posted a tournament rules draft on the Organized Play forums that states for the 2009-2010 season, 10% of a player’s deck may contain foreign language cards. That’s six cards per deck. If you have any Japanese Claydol, Uxie, LV.X Pokemon, etc., then you may use up to six of them in a tournament deck! Basic Energy are counted in the six as well.
However, keep in mind this is only for this upcoming year – for the 2010-2011 season, there is a chance you may not be able to use any foreign language cards at all. POP probably changed their recent decision to ban all foreign-language cards because players already bought Japanese boxes in preparation for next season without knowing what POP was planning. So, this year could be a transitional period to phase out all foreign cards. In other words, be cautious when buying foreign cards for upcoming sets, since you may not be allowed to use them at all next September as was the original plan for this year.