A common saying in German is, "Deutsche Sprache, schwere Sprache", which means "German language, difficult language." It is not surprising that many foreigners get confused by complex German grammar and the construction of seemingly endless sentences.
German is the only official language in Germany. It is also spoken in Austria, Liechtenstein, Luxembourg, large areas of Switzerland and parts of Northern Italy, Eastern Belgium and Eastern France. Around 100 million Europeans speak German, which means that after Russian it is the most widespread native language in Europe and amongst the ten most-spoken languages in the world.
However, you need to be aware that German is not exactly the same everywhere! Even though written language and grammar is uniform across the whole country, there is a wide range of regional accents and dialects. Some dialects, such as Bavarian, are so strong that even Germans have difficulty understanding them. Don't be surprised if you feel completely lost in the beginning when visiting these regions. This variety of languages reflects the wide variety of regional cultures and habits in Germany and is a source of many jokes.
If you've learned German abroad, you're probably accustomed to Hochdeutsch, which can be literary translated into "high German" (note that some Bavarians might not agree to this term). People with higher education are usually able to speak Hochdeutsch (if they feel like it). In smaller villages with less outside contact the inhabitants might have a hard time doing so.
There is a wide belief among foreigners that German is very similar to English, so some people think that if they speak English they will be able to learn German quickly. Without wanting to disillusion you, the reality is that the two languages have far less in common than many people believe. At least at a basic level, it is a lot easier to learn English as you don't have to struggle through complex sentence structures and the widely feared German "cases" (which basically define the role of a noun within a sentence). The fact that many Germans speak very good English might be because, after struggling through their own language, they show little fear of learning another one!
If you're going to study in Germany or read a lot of German documentation or papers, be prepared for a serious shock! Germans seem to perceive the construction of endless and completely incomprehensible sentences as a national sport (ed. before anyone complains, the author of this text is German). Don't be surprised if the introductory phrase of an academic paper is half a page long. You might get the impression that the author deliberately tries to scare you away from reading the rest of the document! Or maybe he just wants to test whether you're willing to spend half an hour decoding this sentence and therefore are able to digest the rest of his deep thoughts!
Despite these little obstacles, we strongly encourage you to learn at least some basic German. Even though you can get by with English in Germany, only when you get to know the language will you be able to get the most out of living in Germany. In order to study, you even have to prove that you have a good command of the German language. The only exceptions are international programs taught in English.
Don't be afraid of making mistakes, since Germans are not as proud of their language as other nationalities (like the French) and are therefore normally very forgiving when it comes to their languages. However, don't get depressed if you don't impress people with your language skills - German don't get excited easily.