You can talk English in Hesse without a problem, but it's better when you speak slowly, as many people are not confident about their English and do not want to embarrass themselves with a native speaker. In smaller towns and out in the country, it's more likely that you will encounter old people who cannot speak or understand English.
However, as students take English as a second language, you'll find that almost all young people speak English well, albeit possibly accented. Even slightly older people usually do have at least some command of English, and in the cities you should not be surprised to find a 60 year old who speaks English quite well.
You may be surprised at how friendly the people can be, as (like most Germans) the Hessians are very friendly and nice when you are friendly too.
You can get some good tips on local events and places to visit from the locals if your take the time to ask.
Feel free to try out any German you have--either you'll get what you want, or at the least impress/amuse your victim!
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.
International visitors will arrive mostly at Frankfurt Airport, the second largest airport in Europe and a major hub for the German carrier Lufthansa. It's the most important Hub for all Staralliance Airlines (such as United (US), Austrian, Swiss, Thai, Singapore, AirChina, ...). Most major cities in the World are nonstop connected to Frankfurt. The "AirRail" Station or "Fernbahnhof" at the airport (near Terminal 1) is a Train Station for Long Distance Trains (Cologne, Stuttgart, Paris, Amsterdam, Düsseldorf, Brussels, Munich). Frankfurt's central station "Hauptnahnhof" is 15 minutes away by suburban trains that run 24/7 (Lines S8, S9). These also serce cities nerby such as Mainz, Wiesbaden, Offenach, Hanau.
Hahn, Ryanair misleadingly officially called "Frankfurt Hahn" even though the city is over 120 km away, is a former military airfield outside of Hessen being used by "no frills" low budget airlines such as Ryanair or Wizzair. Getting from Hahn to Frankfurt takes about 90 minutes by bus or car.
Regular and high-speed InterCityExpress (ICE) connect Frankfurt and Hesse to the rest of the nation as well as to various international destinations, such as Paris in 4 hrs, Strasbourg, Vienna, Basel, Zurich, Brussels 3hrs. and Amsterdam in 4 hrs. Once a day italian trains run to Milan, and nichttrains run to Budapest, Moskau and Copenhagen. Most long distance trains serve Frankfurt Hauptbahnhof (Frankfurt Central), Frankfurt Flughafen Fernbahnhof (Frankfurt Airport), Fulda and Kassel-Wilhelmshöhe. Some long distance trains also serve Wiesbaden, Darmstadt, Hanau, Giessen and Marburg. But Most train stations are well connectet to Frankfurt Central. If you travel on long distance trains you should buy a ticket in advance, gernam Railways www.bahn.de sell tickets 90 days before. "Sparpreis" tickets are only valid for the itinerary printed on the ticket. If this says "+NV" or "+City" you can take any other Subway, Suburban or local train (RB, RE) to catch your long distance train. If you buy a "Flex Ticket" the price is fixed for one route and you're flexible to take any train on this day and route.
There are large regional networks of public transport:
"Hessenticket" for day-long on Local trains in Hesse and Mainz for up to 5 people.
Local specialties include wine from grapes, especially white grapes, and from apples (a kind of cider). This apple wine (Ebbelwei or Ebbelwoi) may be enjoyed straight (pur) or mixed (gespritzt). The latter versions distinguish between "sweet" and "sour", i.e. mixed with either some citrus soda (Süßg'spritzter) or sparkling mineral water (Sauerg'spritzter).
Across the state and the country is a dense network of Youth Hostels (membership required).
Good luck if you're out of the major cities like Frankfurt or Wiesbaden.
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.
The number for the Police (Polizei) is 110, and for the fire department (Feuerwehr) and ambulance service 112. They can often speak some English.