In a way, the advertisement is true that one will be able to speak English fluently in three months.
But this is limited to things like self-introductions.
ご質問ありがとうございます。
"In a way,"＝「ある意味では」
"the advertisement is true"＝「広告は正しいです」
"that one will be able to speak English fluently in three months."＝「3か月で英語を流暢に話せるようになるとは。」
"But this is limited to things like self-introductions."＝「しかし、これは自己紹介などに限られています。」
ご参考に。
アメリカ合衆国 
