What are the reasons for the introduction of new anglicisms into current German? Could someone please summarise the state of the scientific literature on that phenomenon?
German has a very valuable and useful feature, that some other languages don't have: You can enrich it with words from other languages. (As far as I know you can't do this with Icelandic and with many other languages.) So, when there is a word in another language, that has a meaning that a German word doesn't have, you can introduce this word into German language and use it as if it was German. If you want, you also can use a synonym from another language, that has the same meaning as a German word.
The first step is to use it as a foreign word (Fremdwort): If it's origin is a language that is written with latin letters (Spain, Polish, Hungarian, ...), you use it's basic form with the original spelling, only if the word is a noun, it's first letter is written in uppercase. Words from languages with other writing systems (Russian, Chinese, Arabic, ...) are used in the official transcripted form. Also the pronunciation is as close to the original spelling, as it is possible for German native-speakers. But still in this phase you inflect and decline those words with the rules of German grammar. Nobody who uses foreign words needs to learn foreign languages grammar.
Some examples: Spaghetti (Italian), Friseur (French), Kaftan (Arabic), Chuzpe (Hebrew), Hazienda (Spain)
The second step is to use the word as a loanword (Lehnwort): The spelling is changed to match the German rules for the mapping between sounds and letters (bureau → Büro) and the pronunciation is even more German-style.
Some examples: Frisör (French), Kaffee (Arabic), Jubiläum (Hebrew)
The last step is to interpret a word that was adopted from a foreign language as an inherited word (Erbwort), i.e. it's status is that of a word, that "always" was German.
Some examples: Fenster (Latin), Zucker (Arabic), Sack (Greek)
The classification as foreign word, loan word or inherited word is often unclear. Some people might say, that Fenster, Zucker and Sack are loanwords, because they don't origin form some proto-germanic languages. But I think, that 99% of all German native speakers are not aware of the fact, that those words were imported from other languages, so I would count them as inherited words.
Also the border between foreign words and loanwords is very blurry, as you can see on many words with a french origin like my example from above (Friseur, Frisör)
So, what is so special about words that are imported from the English language?
I would say: nothing, except the time when they were imported.
German contains thousands of words with a Latin origin. Most of them were imported many centuries ago, in an era, when the bible was available only in Latin and when educated people used to correspond with other educated people from other languages in Latin. The same is true for (ancient) Greek.
Then, there are also thousands of words with a french origin. Most of them were imported in the 18th and 19th century, when it was considered noble to speak French.
Today we live in an epoch, where it is important to have international contacts, and where it is important to be able to communicate with people from other countries. And you need a language for this international communication. Long ago, this international language was Latin. Then it was French, for some purposes also Italien and German too. (Think of all the German loanwords in English language, many of them in scientific context: eigenvektor, eigenvalue, aufbauprinciple, but also: doppelganger, rucksack, leitmotif, kindergarten, poltergeist, ...) But now this language is English, and the need to speak an international language never was more important than now.
So, everybody who grew up in West-Germany and Austria, and who was born after world war II had to learn English in School. This is why today almost everybody in this region speaks English. So today, English is a language, that German native speakers are very firm with. So, today German has is a very intense contact with English. Maybe even stronger than the historic contacts to Latin and French ever have been.
So, it would be very strange if we had not tons of English words entering the German language.
Very brief answer:
English is the Latin of the modern age, a lingua franca. Many topics are discussed in international environments (science, politics, tourism, etc.)
Due to the cultural hegemony of the English speaking world (Holywood, etc.) everybody is exposed to English, and usually in contexts that are understood as being positive. Using English terms is therefore seen by many as "cool".