Get the contract in german beforehand. Get someone to translate /go through it for you sowly - make notes, ask questions etc. One you are happy you can go to the Notariat and essentially make sure the contract is the same as the one you've been through. And take someone along you trust who speaks German. Don't trust the agent to do any assistance or translating or accept any 'oh that's normal here' etc
In our case the contract was based on standard text generated by the Notary based on a form found
here to fill in with the details ("Formular für die Übermittlung von Kaufvertragsangaben") and the Notariat makes the actual contract from that - you could maybe get a copy of that as well from the Notariat in advance so you can see what the other side has proposed, especially where there are choices etc. You can also then notice any extra sections etc added that weren't in the form. In our case the agent was a pain and the Notariat wonderfully helpful in the days leading up to the signing, with lots of docs being emailed around for review etc.
Be aware also that any Reservation contract with deposit etc is not legally binding (on either side). Although they are common practice we refused to pay tens of thousands of CHF's to a third party based on a non legally binding contract, where they have a big chunk your money and then negotiate contract terms. The
only legal contract for a house purchase is the one done at the notary.