there isn't an official way of doing that, but.
you can download this mod: http://18.104.22.168/ett.php
it's from xentelian.
my game was in Portuguese(that i speak, BTW, but the translation was very badly done) and afetr i downloaded his mod, my game is in English. as he says on the site, it does have some changes from the normal english game.
the only things that are still in Portuguese are sounds and things with ramdom names(like forts)
BTW, the site's IP keeps changing, so if the link doesn't work, just look for xentelian on google
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