accidents
The number for the Police Polizei is 110, and for the fire department Feuerwehr and ambulance service 112. They can often speak some English.
telephone
Public telephones are rare in many areas, and to complicate matters there was a transition from coins to rechargable/disposable cards a few years before mobile phones made public telephones mostly obsolete. You can buy public telephone cards at the Post or some shops. If you have a mobile phone that takes SIM cards, consider buying a disposable SIM at a mobile phone shop. In the case of an emergency, most people would let you use their mobile phone.
internet cafes
Good luck if you're out of the major cities like Frankfurt or Wiesbaden.
talk
German is the main language in most of the state, although Hessian, the local dialect, is spoken natively by many rural and old people and can sound quite different from standard German. However, since almost all Hessian speakers also speak standard German and most people also speak at least rudimentary English you shouldn't have any problems communicating with them.