German dialects
German is one of the world's major languages, spoken by more than 120 million people, only two-thirds of whom actually live in Germany. When people speak of the "German language" today, they are likely thinking of the standard German that is the official language of Germany. What may not be understood by many non-Germans is that most people born in Germany today do not learn the official High German, or Hoch Deutsch, as their first language. Instead, families at home tend to speak one of several regional dialects, such as Bavarian, Swabish, Thuringian, or Brandenburgish. Only when they begin public school are German children forced to use the official language.
High German versus regional dialects
There are approximately a dozen regional dialects within modern Germany, and a few more in surrounding countries such as Switzerland. For practical purposes, the regional dialects are different languages since they are not mutually comprehensible, although neighboring regions can understand each other a little easier than distant regions. High German was invented in the late nineteenth century after the different regions were finally united politically under the Kaiser. The spoken version of official High German was a compromise that drew heavily on the dialects in the middle of what is now Germany, to minimize the amount of adaptation needed for the most people. Similarly, for American English, a midwestern accent (from the middle of the country) is the preferred TV newscaster dialect.
High German has been successful at encouraging a national identity and fostering inter-regional communications. However, native Germans can often tell from what region a person hails immediately from that person's high German accent, since many people do not lose all the traces of their original dialect. TV stations in Germany today still run some programming in the local dialect.
There are many other dialects of German which grew up in communities living outside of the country. For example, Yiddish--spoken by many Jewish communities around the world--began as a dialect of German. Many Hebrew words were added to it, and vast regional differences also arose. Similar, in South Africa which was formerly a colony of Germany, a dialect of German called Afrikaans incorporated many new words and concepts from South African native tribes, but its basic grammar is still German-like. The Pennsylvania Dutch language in the United State may be considered as yet another dialect of German. Aside from the expanded, specialed vocabularies, these three German dialects--Yiddish, Afrikaans, and Pennsylvania Dutch--are only about as different from the official high German language as the other regional dialects within German.
In fact, although it is perhaps politically unpopular to say so, the Dutch language started out as "just another" regional dialect of German, about the same "distance" from official German as any other of the regional German dialects. But since Holland and its surrounding German-speaking areas were not permanently annexed into modern Germany in the late nineteenth century, Dutch speakers were not constrained to adopt official German, and indeed, due to the invasion of the Netherlands by Germany during World War II, Dutch is now fiercely claimed by many to be a language distinct from German.
Germanic language family
The grammar of modern German (and its many dialects) grew out of Middle High German in the Middle Ages, which in turn grew out of Old High German in the Dark Ages. Historically, "high" meant areas that are in the mountainous regions (southern Germany, for example) as apposed to geographically lower-lying areas around the North Sea. For example, the Netherlands (Die Niederländer in German) means "low lands".
There is a larger "Germanic" language family which includes English, Icelandic, Danish, Norwegian and Swedish. Germanic languages are Indo-European languages that share common underpinnings of grammar and vocabulary. Germanic languages all share, most especially, similarities in the 500 or so "core words", which are the words which children typically learn first as they acquire language. These include words such as mother, father, the parts of the human body, the names of everyday animals, and common actions such as walk, run, or sleep.
Active word-building capacity in German
Although English is a Germanic language, it now differs from the German dialects in its extremely large vocabulary expanded from many different languages such as French, Latin or Spanish. Translators trying to render German into English may find a dozen English synonyms, of only subtle (if any) difference in meaning, as compared to a single word in German. This has made translating the works of Sigmund Freud, just for example, particularly difficult; any two translations may contain almost completely different terminology in English. Thus, scholars are encouraged to attempt to read such thinkers in the original German if at all possible. In fact, English nowadays sports a huge unabridged dictionary, but German does not have need an unabridged dictionary, due to its relatively smaller vocabulary and to its active word-building capacity.
Most vocabulary in German is in fact built up by compounding two or more of the core words together. The meaning of such words is generally obvious to children as they acquire language, and they do not need to look up words in a dictionary nearly as often as English-speaking children do. For example, in English we have the term "glove" but in German, that is HandSchuh (hand shoe). If children already know Hand and Schuh, the they don't have to be taught what HandSchuh means the first time they hear it. Building on this, in English we have the term "glove compartment" in reference to cars. In German, that is HandSchuhFach (hand shoe box), and in the context of a car, that is immediately clear in meaning, whereas English-speaking children must first learn the Latin-derived word "compartment" before "glove compartment" makes any sense.
Another example is the word "superficial" in English; many English-speaking children must explicitly be told its meaning at first. But the German equivalent of superficial is überflächlich ("over" + "flatliness"), and its obvious meaning to Germans is "skimming over the surface".
In mathematics, English speakers must learn arcane terms like "apex", whereas German speakers encounter "Spitz" ("peak", the same word used for mountaintop). This reliance on building larger or broader concepts out of its core words has made German a particularly elegant language for mathematics, as little Latinized vocabulary need be learned.
Relative ease of learning German for native English speakers
German is considered one of the most accessible foreign languages for native speakers of English to learn. This is due to the similarities of core words and grammar in the two languages, but also to German's reliance on compound words built from simple ones. To an English speaker, Spanish might seem easier initially because it has shorter words, but Spanish has a much larger "different" vocabulary which English speakers must learn. German, on the other hand, builds most of its extended words from its core words, so acquisition of sufficient German vocabulary by English speakers can occur much faster than for many other foreign languages.
Testimonials of American soldiers serving in Germany in World War II showed that American soldiers were able to pick up substantial amounts of German in only a few months without any formal training, just by hearing a lot of it spoken in real-world situations. This may well be a consequence of the close similarity of the core words of the two languages.