"영어로 말 합시다" => 영어로 말합시다 ("말하다" is the base form). 합시다 is a formal sentence ending for making a light proposal, similar to "Let us...". Here's a family of such endings: - 합시다: formal, used between adults. - 하자: informal, used among kids, or between close adult friends. - 하지(요)?: a weak and soft question form of a proposal. - 할래(요)?: a stronger question form which can be used to make a proposal. - 할까(요)?: similar to 할래, but slightly weaker. * 하지?, 할래?, 할까? have other uses too, like simply asking the other person's intention, so the context and right intonation are important for making the meaning clear. Examples: - 이제 그만 (좀) 합시다 / ..그만 좀 하자 - Let's stop it now. - ..그만 좀 하지(요)? / ..그만 좀 할래(요)? / ..그만 좀 할까(요)? - 점심 먹으러 갑시다 / 점심 먹으러 가자 - Let's go have lunch. - 점심 먹으로 가지(요)? / 점심 먹으로 갈래(요)? / 점심 먹으로 갈까(요)? - 영어로 말합시다 / 영어로 말하자 - Let's speak in English. - 영어로 말하지(요)? / 영어로 말할래(요)? / 영어로 말할까(요)?