The 19-year-old striker became available after RC Strasbourg were forced to release a number of players due to financial problems.
"He's a really exciting talent," Latics manager Roberto Martinez told Sky Sports News.
"He's a young man, and we want to develop him and try to fulfil his potential, which is huge. Those are the signings that are going to take the club forward.
"It's unfortunate because you don't want to see football clubs going bankrupt but those situations happen. We were quickly aware of his talent and we are delighted that he's chosen us to develop his career," he added.
Dicko is unlikely to make his Wigan debut this weekend, when Norwich City visit the DW Stadium.