Twente revealed Mokotjo, who cost a reported €1.5 million from PEC Zwolle, attended training this morning and will wear jersey number 22 at De Grolsch Veste.
The 23-year-old joins compatriot Nhlakanipho Ntuli at The Tukkers, with the latter competing for the youth team.
Twente moved to bring Mokotjo on board - amid rival interest from Ajax Amsterdam - following the sale of Quincy Promes to Spartak Moscow for €15m.