The official English Pokémon website officially revealed Pokémon TCG: XY Flashfire, the second XY English based Pokémon Card Game Expansion set on March 26th, 2014. It was released on May 7th, 2014. Images from the press release have been added to an Imageboard thread.

Press Release - Pokémon TCG: XY Flashfire available in stores on May 7, 2014

Pokémon TCG: XY—Flashfire is the latest expansion to the Pokémon Trading Card Game franchise. Booster packs and theme decks will be available in stores on May 7, 2014, bringing more than 100 new cards to collect and play.

Blaze your way to glory and watch the sparks fly when you battle with cards from the Pokémon TCG: XY—Flashfire expansion. Ignite the action with a firestorm of Fire-type Pokémon and watch your opponents’ terrified double-take as the awesome Mega Charizard-EX makes its scorching debut in this breathtaking expansion. Your explosive adventures will continue as your foes flee the field with certain doom flashing before their eyes! The XY—Flashfire expansion contains over 100 cards, including five new Pokémon-EX and three new Mega Evolution Pokémon.

Key Features of the Pokémon TCG: XY—Flashfire Expansion:

• Three new Mega Evolution Pokémon — The expansion features two powerful versions of Mega Charizard-EX (a Dragon-type Mega Charizard X and a Fire-type Mega Charizard Y), in addition to Mega Kangaskhan-EX.
• Five new Pokémon-EX cards and four new full-art Pokémon-EX rare Ultra cards—New Pokémon-EX cards include Charizard-EX (two versions), Toxicroak-EX, Magnezone-EX, and Kangaskhan-EX.
• New Pokémon—Over 25 Pokémon from the Pokémon X and Pokémon Y video games appear in this set, in addition to 15 Pokémon that appear in the Pokémon TCG for the very first time.
• 15 new Trainer cards including three new full-art rare Ultra Trainer cards—New Trainer cards bring increased depth and player strategy to competitive battles.
• Booster Packs—Packs of 10 additional cards selected from the expansion will be available.
• Theme decks—60-card preconstructed decks are designed to introduce players to the Pokémon TCG by enabling them to play right away.

Source: http://www.pokemon.com/us/pokemon-tcg/xy-flashfire/explore-and-watch/