I have flown for a year in Terlet at the Gelderse Zweefvliegclub. It is a big structure, they accept english speaking pilots, you can contact the club directly on the website. The club is very active on the week-ends but most of the instructors are flying with students so not sure you can easily get a ride. They fly on week days but you need to book the gliders with the club. You need a valid pilot licence including your medical to fly with them. They mainly use winch launch but they can also provide tow rides.

Their fleet is quite nice with 3 Duo Discus, 1 LS8-18, 1 ASG29, 2 LS4, 2 Discus and 3 ASK-21 all equipped with state of the art LX8000/9000 and FLARM. Gliders are well maintained and well flown so no issues there.

Terlet is a nice place to fly with nice getaways in Germany. I have flown a 500k last year with 2000m+ thermals and amazing conditions, you can't go wrong. It is not on the shoreline so it is not so much subject to maritime entries and you can easily fly XC.

Contact Ton Kleverwal he can definitely help you.

Happy flights!