It should be possible to subscribe to the service as long as you have a SEPA zone bank account. That would require to deal with a bit of paperwork that is only available in french language. You might be better check with the company you choose before sending contract.
Disclaimer : I have included several links to a company that offers such subscription. These are examples. Other companies might have better offers. I am not affiliated with this company in other way than being actually subscribing to their télépéage offer.
The official name is liber-t, which is the label under which several companies operate the system. You can subscribe to any company that is a member of this group.
Notice that besides online subscription, you also can subscribe on premises.
Does it make sense to use it ? : If your goal is saving time at toll barriers, it is a good option. Some lanes are reserved for badge users, so even in the busy days, you will have a shorter waiting time using these lanes as there are less users and the average passing duration is shorter. Now, if this is for a few days a year, only you can balance the cost and hassle with the added value. You can always pay with a chip Visa (and probably Master) card at the toll gate, which can be quite fast, but you don't have the benefit of the reserved lanes. Be also aware that in case of system failure (be it your transponder or the toll gate itself), you will have to get into vocal communication with a (probably) french speaking operator. You usually will have to spell the (long) id number printed on your badge.
Some answers are :
I couldn't find english or german translation on several major télépéage provider websites.
Reading terms of service from a major provider, there's no mention of nationality or place of residence. What they require is that you have a bank account in the SEPA zone.
It is based on a subscription model. There are various offers. One option is pay only when you use. The monthly subscription is only due on months where you actually use the badge. No deposit. Another option is all year use. You pay a (slightly lower) fee every month. There's a deposit fee of 30 €. For both these options, you will have to pay the delivery fee for the badge. On the mentioned website, delivery fee outside of France is 15 €.
Only payment option seems to be through a direct debit on a SEPA account.
There are no discount fee when using a badge (Actually, you are paying the subscription in addition to the toll fee). If you were to do a daily commute on a given segment, there might be a discount, depending on various parameters.
The badge can be transferred to another vehicle as long as it is in the same vehicle category (classe de véhicule).
As there are offers explicitly targeting this use case, you should be able to use the badge only once in a while. Notice nevertheless that the above mentioned (pay only as you use) offer mentions that if you do not use the badge for 14 consecutive months, the 15th month will be charged, wether you use the badge or not.