There are no restrictions for non-german citizens.
You can participate in a guided tour and you can even watch a debate from the tribune of the reichstag for ~1 hour. You need a reservation for that, but you can do this online (see the link above).
You need a reservation too, if you want to go to the dome (“kuppel”) and the roofgarden (“dachterrasse”), but this is included in some of the offers available I believe.
You may also visit a congressman with a group of >10 visitors, but you will need an early reservation for this.