The official Pokemon TCG website has posted a policy change that affects players that use cards from other countries. Only cards that match the language of your country will be allowed to be use in premier events. The policy change goes into effect September 1, 2009. Below is the press release from the official site.

Over the course of several seasons, Pokémon Organized Play has noticed a sharp increase in the use of foreign-language cards in markets where those languages are not commonly understood by the player base. While we recognize that the Pokémon Trading Card Game is an international game, the unfortunate side effect of this increase is that it has added a layer of complexity to an already complex tournament setting at Premier Events. In cases where the majority of players and event staff are not fluent in these other languages, the pace of games has slowed due to translation issues, even with the use of the Card Dex or local-language reference cards.

Starting with the 2009–2010 tournament season, which begins September 1, 2009, Pokémon Organized Play will restrict the use of foreign-language cards at Premier Events, based on where those events take place. The Pokémon Trading Card Game is currently printed in English, French, German, Italian, Japanese, Portuguese, and Spanish. As English-language cards are distributed in the vast majority of markets worldwide, and more cards are printed in English than in any other language, English cards are legal for Premier Events in every market.

In Special Premier Events that encompass multiple countries, the Last Chance Qualifier, and the World Championships, players are permitted to use cards in any language listed for their home market during these events, regardless of where the event is held. Players from markets where a language is not listed under their country of residence are not permitted to use those cards. For example, a Canadian player may use English or French cards in the World Championships, but may not use German, Italian, Japanese, Portuguese, or Spanish cards.

This new rule will not affect the legality of foreign-language cards at non-Premier Events and Leagues.

Source: http://www.go-pokemon.com/op/news/articles/51.html