English language has become  very important for  all countries in Southeast Asia.

From  2015 The southeast Asia will be united with ( become part of ) The AEC (Asean Economic Community).
And English language  has become very important for all the  countries in Southeast Asia, 
because English language is the only language that we can communicate to each countries.

Please help me to correct the sentence above.

The English language has become very important for all countries in Southeast Asia.

In 2015, Southeast Asia will be united with the AEC (Asian Economic Community),
and therefore the English language will become very important for every country within Southeast Asia.
It is especially important because English is the only language that we can use to communicate between the countries.

Please help me to correct the sentence above.