Espinoza has been granted a permission to work in the UK.
"He is someone who physically is really capable and has a gifted left foot," Martinez told wiganlatics.co.uk.
"Having someone with such a good left foot gives a balance to the squad because most players are primarily right-footed.
"He's developed his tactical awareness and has learned how to play in different systems.
"Roger can play in any position in the midfield and can even play out in a wide left position, so we are delighted to capture a player with such versatility and stature."