Full Slate offers currency and language support for businesses around the world. To price your services in your country's currency, go to Setup > Company and select your currency. Further, you can use all international characters when you set up your services under Setup > Services, add a company description under Setup > Company, or otherwise add text to your client scheduling pages. Default text is still in English, but this only displays in a few places.
If you choose to receive alerts for new and modified appointments under Messages > Alerts, we support over 1,000 mobile carriers worldwide, so it's very likely you'll receive your alerts. It's best to enter your mobile number under 'my account' in the international format -- plus sign ("+"), country code, then number -- to be sure it will work.
You can also choose to allow your clients to receive SMS (text message) reminders, and as long as they use one of the 1,000+ supported carriers, they will receive SMS reminders. See this help page for more on SMS reminders.
The mobile numbers on your client profiles (under the Clients tab) do not need to include your country code. Rather, as long as you designate your country under Setup > Company, Full Slate will automatically include your country code when sending SMS reminders to your clients. If a client record has a country code included, then Full Slate will not add the country code. So SMS reminders should work whether or not your client records include country codes.
So for example, in Australia, a client's mobile number could be entered with the country code as +61 455 555 555, or without the country code as 0455 555 555.
For more, please see http://blog.fullslate.com/2011/04/07/full-slate-goes-international/.