Van der Merwe, who has made three appearances for the Springboks, will join his Sharks team-mate Robert du Preez and Springbok compatriot Faf de Klerk at the English club.
The hooker is currently joint top try scorer in the 2019 Super Rugby competition, with three tries to his name in two games.
"I feel the time is right in my career for a move away from South Africa," Van der Merwe told the Sale Sharks' official website.
"I have just started a family and after considering all my options with them, I feel this is the best one to take for us as a family. I am good mates with Faf De Klerk and having spoken with him, he only has good things to say about Sale so we are really excited about joining the club and experiencing a new lifestyle in Manchester.
"For the meantime though, along with Rob I am fully committed to the Sharks and I will be doing everything I can to be as successful as possible in my final season in Durban," said Van der Merwe.
READ: Robert du Preez quits Sharks ... for Sharks
Sale Sharks Director of Rugby Steve Diamond was delighted to secure the services of Akker ahead of next season.
"In order to really compete in this competition, you need to have two good options in most positions and we are specifically targeting forwards with our recruitment drive this year so I am delighted to announce the signing of Akker. He is a world class player and he will be an excellent addition to the squad alongside Rob Webber," he said.