Latics reserve-team regulars Holt and Routledge, both 20, have joined Swedish side Ostersunds on loan until July.
Roberto Martinez believes the move will form an important part of the players' development and has urged them to use it as the next step towards breaking into Wigan's first XI.
"Jon and Joe are two very promising youngsters who have been playing well in the reserves," Martinez told the Wigan Evening Post.
"Reserve-team football gives you a certain challenge, but they have gone beyond that - and there is still a massive gap to the first team.
"It will be great for them to play abroad and fulfil important roles at a club and continue their development. For them to go abroad and mature as human beings will be a unique experience, and exactly what they need."