English is widely understood in tourist areas and to a very limited extent in rural areas. It's best to double check before plugging anything in. A torch is a useful item to have as power cuts do occur. Plugs are two round pin. Water Tap water is not safe to drink and ice cubes should be avoided.
Bottled water is widely available.
Health Reasonable medical facilities are available in major towns but once outside these areas, medical services tend to be very poor. Make sure that you have adequate health insurance that covers evacuation and consider inoculations against typhoid, cholera, Japanese encephalitis and hepatitis. There is a risk of malaria in many parts of Indonesia and it is recommended that you take advice regarding anti-malarials. It is always best to check the current situation and any vaccination requirements with your doctor when planning your trip. There are numerous domestic airports all over Indonesia providing a vast network of travel options.