Schmeltz has played in his homeland for Willem II, Almere City, Sparta Rotterdam and SC Veendam.
The 24-year-old became a free agent in March when Veendam filed for bankruptcy and released him from his contract.
Latics boss Lee Johnson told the club's official website: "Sidney is the perfect character and just the sort of player we are after.
"He is quick, exciting, skilful and hungry to learn the English game. It is our job as coaches to teach him that."
Schmeltz becomes Johnson's third signing ahead of next season, following James Dayton and Johnson Clarke-Harris into Boundary Park.