Lingua franca = a language used for day-to-day public communication, which is not the speakers’ own language.

• English is a lingua franca in a lot of countries nowadays.
• English is the lingua franca of the literate in India.

Jog someone’s memory = cause someone to remember something suddenly.

• I tried jogging mom’s memory , but she couldn’t remember Joe’s phone number either.
• I tried to jog Bill’s memory about our childhood antics.
• Maybe this photograph will jog your memory.

In/within living memory = within or during the time that is remembered by people still alive.

• The worst recession in living memory.
• There hasn’t been a blizzard like this in living memory.
• These are the worst floods in Kerala within living memory.