The -s plural marker is not a foreign import into the German language
The Anglicization of the German language can be seen throughout the country and is often disparaged as a form of foreign infiltration. It is indeed true that ever more English words are finding their way into everyday German language, as Germans often book an "Adventure" Urlaub (vacation), buy an "Outdoor" Jacke (jacket), ride a "Bike" instead of a Fahrrad, and talk about baking a "Cake" rather than a Kuchen.
"The Anglo-American influence has certainly increased since the Second World War," confirms Professor Dr. Damaris Nübling of the German Department at Johannes Gutenberg University Mainz. However, the German plural formation by adding an -s suffix such as with CDs and DVDs, Pkws (cars) and Lkws (trucks), along with Limos (soft drinks) and Kuckucks (cuckoos) is not part of this process even though most Germans seem to think so. The usage of the -s plural marker has nothing to do with English; it is purely German in origin. "The -s plural first appeared with names like the Müllers and the Schmidts, i.e. the Müller and the Schmidt families, long before we Germans started to borrow English words," explains Nübling. A nice example of an early German plural formed using the -s suffix is Thomas Mann's novel "Buddenbrooks," a title which was definitely not borrowed from English.
According to Damaris Nübling's historical research, plural formation with the -s ending first appeared in the 17th/18th century, initially in family names and a little later for first names and place names. It can be traced back to German -s genitive suffix. Müllers Familie (Müller's family) or Meiers Leute (Meier's people) are examples. A shift in meaning over time turned the -s suffix signalizing the genitive singular into the plural -s. A mixed form, a linguistic archaeopteryx, as in the dialect usage "'s Müllers sin do" the abbreviated form of "des Müllers Leute sind hier" (i.e. "the Müllers are here") can still be heard in some dialects spoken in southern Germany.
"The reason behind the usage is to prevent the name itself from being distorted," explains Damaris Nübling. "A name should change as little as possible." Minimizing the change is most easily done using the -s suffix as the name remains constant and is not distorted as it would be with other Germany suffixes. Not only names but also abbreviations need to be recognizable in their plural form: Unis (universities), Studis (students), Limos (soft drinks), MTAs (Med-Tech Assistants), and CDs. The German language is rich in such abbreviations, whose meaning is not always known and which are often difficult to memorize, because people are not always aware of their full form. In such cases the -s plural makes it easier to recognize the original form and maintains the structure of the word. The same applies to onomatopoetic forms in German such as Kuckucks (cuckoos) and Kikerikis (cock-a-doodle-doos), to nominalizations in German such as Aufs und Abs (ups and downs), Wenns und Abers (ifs and buts), and Ahas, as well as to non-Germanic words common to the language such as Pizzas and Kontos (accounts). Once the word has attained sufficient awareness, the plural -s suffix is replaced by the more common -en suffix as with Pizzen and Konten. It is a "transitional plural," used until the foreign word is fully integrated into the language.
"The -s plural is genuinely German. It does not have its origins in the English language and is not being re-imported," summarizes Damaris Nübling. If anything, Germans tend only to integrate English lexemes, i.e. entire words. They do not normally integrate single grammatical elements from the English language. Grammar always has deep roots within the language system and is not so easily changed through contact with other languages. Furthermore, the use of English words is often completely justified: When we adopt a new object from abroad such as the computer, it is only natural that we adopt the designation along with the object. It has always been so: The German words Mauer (wall), Fenster (window), Tisch (table), Keller (cellar), Speicher (store house, storage) are from Latin as they were the products of ancient Rome. "There is a need for English expressions, but their influence on the German language is generally overestimated," says the Mainz linguist.