I thought she was acting foolishly, but I 'bit my tongue' [='held my tongue'] and didn't say anything.
The news of their engagement 'set tongues wagging'. = 'Tongues were wagging' over their engagement.
He speaks English fluently but his 'mother tongue' [='native language, first language'] is Chinese.
(..) "Your doom is near at hand. Isildur's Bane is found." Isildur's Bane. Boromir! Never before has any voice uttered the words of that tongue here in lmladris. I do not ask your pardon,Master Elrond... ...for the Black Speech of Mordor... ...may yet be heard... ...in every corner of the West! (..)2001 The Lord of the Rings: The Fellowship of the Ring
(..) It's some form of Elvish. I can't read it. There are few who can. The language is that of Mordor,which I will not utter here. Mordor! In the common tongue,it says: ''One Ring to rule them all... ...One Ring to find them... ...One Ring to bring them all... ...and in the darkness bind them.'' (..)2001 The Lord of the Rings: The Fellowship of the Ring