I have googled a bit, but cannot find a standard termination letter for a flat. Is there anything wrong with writing one in English?

We are with Basler Versicherungen, and they did understand English when we moved in :-)

just write it in English or have a work-colleague run through the one-liner that it needs to be.

Don't forget to send it registered

See the similar threads below - I think it's been done.

We just sent in our termination letter to Basler as well, they accepted what we sent as we received our moving out package over the weekend

It said:

Kündigung

I XXX (name) would like to give our notice for the following items. We are planning on moving out on the X.X.X. (date)

- Apartment XXX (address), Xth floor, X rooms,
- Parking space X at XX (address)

Let me know if you have any questions.

Thank you,
XXX

I can be contacted during the day to arrange visits at XXX XXX XXXX (tel. number)

*Wir möchten unsere Wohnung and Parkplatz kündigen per X.X.X. (date), sie sind am XXX (address).

The first download on this page from the Aargau Mieterverband is what you might be looking for, just correct as necessary.

http://www.mvag.ch/downloads/downloads.html

Note that by law, if you apartment/house is a family dwelling, your spouse MUST sign the termination letter as well!

how do you send the letter "registered"?

If I go to the post office to send it, does that count? or i need to ask for something special...

thanks!
cecilia

do you speak Italian?
if not, when you hand the letter over, make a signing action with a pen. They'll get it

In Italian you ask for "Raccomandata"

(German: Einschreiben / French: Recommandé)