Planning to visit Tanzania is a great choice! First thing to do is to ask for a touristic Visa before leaving: you can contact the Tanzanian Embassy or Consulate in your country. In this way you will avoid annoying queues at your arrival and save your good humour.
The spoken languanges are Kiswahili, English and a non-specific number of other languages (every tribe has its own one) that we won’t absolutely take into consideration for obvious reasons. After years of practice I am still fighting with Kiswahili: I will probably go on fighting for the rest of my life, but it is such a beautiful and strange idiom that learning it is a real challenge. I am positive though.
The currency is the Tanzanian shilling and it is used in shops, gas stations and for commerce in general, but change offices are everywhere and you will not have problems with euros or dollars printed after 2006.
The best periods for visiting Tanzania are during the dry seasons:
February and March in winter, July and August in summer, even if seasons are opposite under the Equator. Temperatures in February and March can be really hot and really cold in July and August. During the rainy seasons a safari in the National Parks is awfully hard.
Electricity is a big problem: there are regular blackouts during day and/or night hours. The consequences can be easily imagined. No internet connection, no shower. Nothing can be done for the internet, but look at the bright side: you can fully enjoy your holiday forgetting completely your home stress. The shower can be faced with a bucket of hot water: adventure at its best! Unless, of course, you booked a four stars lodge which runs on generators.
Tourists are normally scared about what they read concerning crime: apart from Dar es Salaam, like apart from all big cities in the world, crime concerns theft, so just keep an eye on your bag while you stroll in crowded places and go out in the nights with a local person.
One last general info on tips: no one obliges you to give any tip, but, if you are satisfied with the service, a little sum will be appreciated. You would be kind, they would be happy.