If you want to accompany a learner driver, you must:
be at least 23 years of age and have held a licence in the same category of the vehicle you're driving for at least 3 years.
Holders of probationary driving licences are not entitled to accompany a learner driver.
When out on the road, you must:
ensure that the person you are accompanying drives safely and respects the rules of the road and be able to reach and apply the hand brake easily (except when on practice ground, or when reversing and parking).
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.
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.