According to the official twitter, the second season of Kyoukai Senjou no Horizon
was announced to be aired from the summer of 2012. The battles against England and Tres Espana will be animated.
In the first season, the first 1,308 pages of the original novel (Vol.1 Part 1 and 2) has been animated. The second volume (Part 1 and 2) is total 2,052 pages long. (The third and the fourth volumes are 2,458 and 2,395 pages long, respectively.)
Source: Horizon official twitter
Kyoukai Senjou no Horizon 2