Been 3 times with my son.
Standard German stadium - so out of town with bus links every minute from Moenchengladbach (MB) train station. Your local public transport for a period before and after the game is covered in the ticket price. Once we went to a Dortmund home game on the Friday night and stayed there. Train on the Saturday to the game at MB (a journey of over an hour) was covered by our match ticket. Bargain.
There is a big outdoor eating and drinking section outside the ground. If it’s a half decent day I would get there early, drink outside the ground and chat to their very friendly fans who generally speak decent English.
The first time I went to Gladbach, me and my son got talking to some of 20-25 year old fans on the bus back to the station. They invited us to their Fanhaus (a grand name for the bar by the train station) where the tune that was most played was a tribute to their rivals “Koln, Koln der schisse von den Dom”. And the young lads slipped drinks to my underage son whilst I was in the loo….
Frankfurt do have a significant Ultra following who produce an excellent atmosphere. So it should be a good day out. I have never seen any trouble at Gladbach home games,
Enjoy the game and the day!