22-year-old Taïder joins on a season-long loan from the Italian outfit, with Dani Osvaldo moving in the opposite direction on the same basis.
Both transfers have independent options should the respective loaning clubs wish to make either move permanent next summer.
French-born Taïder played in two of Algeria’s games at the 2014 FIFA World Cup finals, including their narrow second-round defeat to eventual champions Germany.
Prior to joining Inter last summer, the playmaker had a two-year spell with Bologna, where he played alongside future Saints teammate Gastón Ramírez. He started his professional career with French side Grenoble.
First Team Manager Ronald Koeman said: “It’s part of our philosophy for the club to bring in talented young players who like to learn and develop themselves, and that’s true of Saphir.
“First of all, he is a talented football player. He’s 22 and has already played for Algeria at the World Cup.
“I’ve spoken to him about the positions he can play in, and it was a good meeting because he showed me real ambition.
“He can play as a controlled midfielder, but he can also move up around the box and up front, which is a good thing for a coach or manager because it brings more possibilities to the players in the team. He brings competition to the squad.
“He can still learn some things, so we will train him and develop him this season. Over the course of the year, we will then make a decision about the future of the player.
“He’s ten days into his pre-season, so he needs to be in better physical shape but we’ll give him training and he will be ready for the kick-off.
“He will start training tomorrow morning and, depending on how he does over the next few days, we will see whether he will take part in the friendly on Saturday. I will make that decision on Friday.”