The Swiss authorities online
If you want to accompany a learner driver, you must:
Holders of probationary driving licences are not entitled to accompany a learner driver.
When out on the road, you must:
Learner driver are liable for avoidable traffic offences according to their level of driving skills. Accompanying drivers are liable for criminal offences if they are in breach of their obligations.
Neither the learner driver nor the accompanying driver may drive under the influence of alcohol (≥ 0.05 mg/l breath alcohol concentration or ≥ 0.1% blood alcohol concentration).
An 'L' plate (white lettering on a blue background) must be fitted in a prominent position at the rear of the vehicle when driving practice is taking place. It must be removed at other times.
Only vehicles covered by third party liability insurance may be driven.
You are generally allowed to carry passengers, but restrictions apply for certain categories of vehicle:
Provisional driving licences are valid in Switzerland, but not abroad. You should therefore enquire about the rules at the relevant diplomatic representation or customs office.