I didn't think I'd be able to speak English as well as this myself! I've surprised myself!
「ここまで自分が英語を話せるとは思わなかったよ。」＝ I didn't think I'd be able to speak English as well as this myself! I've surprised myself!
「be able to speak 」＝ 話せる
「didn't think」＝ 思わなかった
「ここまで」＝ as well as this
「I've surprised myself」＝ 自分にびっくりしている
イギリス 
