Most often plural forms borrowed from English can get a plural s, and that is probably the most common form:
Wie erkennen Sie, ob es ein Plural-S ist?
Wenn Sie es aber doch genauer wissen wollen: Im Deutschen gibt es keine allgemeingültige Regel wie der Plural (die Mehrzahl) gebildet wird. Der Großteil der deutschen Wörter ändert sich im Plural entweder gar nicht (das Fenster – die Fenster), bekommt ein –e bzw. –en (der Junge – die Jungen) angehängt, enden auf -er und/oder erhalten einen Umlaut (das Buch – die Bücher. Nur ein kleiner Teil der deutschen Wörter endet im Plural auf S.
Nur Wörter, die auf –a, -i, -o oder –u enden bekommen in der Mehrzahl ein S angehängt. Und das sind im Deutschen nun mal nicht allzu viele Wörter. Außerdem enden noch Abkürzungen und Wörter aus dem Englischen im Plural auf S.
Zum Beispiel:
das Foto – die Fotos /
das Auto – die Autos /
das Sofa – die Sofas /
der LKW – die LKWs /
die CD – die CDs /
das Team – die Teams
A plural ending in s is a perfectly viable and legitimate option, in principle:
s-Plural ist kein Sprachimport
Unis, Studis, CDs, Pkws, Aufs und Abs und Buddenbrooks: Pluralbildung auf "s" ist originär deutsch und geht auf 17./18. Jahrhundert zurück
As you can see, even for (supposedly) native German words there is conflicting advice circulating.
But that is the problem here: there is no one-size-fits-all general rule to observe. Unfortunately: it depends. As a native speaker I would listen to how it would sound, if no prior examples are available. And looking for prior use examples would be your best option. Sometimes it seems to be based on real meaning, following from the meaning a word or acronym has in English, sometimes it does not inherit any rules and is treated like a completely germanised word, sometimes it remains a very foreign word.* If you see both variants for ETF, chances are the general opinion hasn't settled yet into a set usage pattern. That gives you more freedom to use it as you see fit (and help shape the generally accepted usage pattern for newly created or introduced words.)
A thoughtful breakdown of intricacies might be worth a read here: German noun plural reconsidered
Still looking for a rule?
1.2.4 The plural ending -s
The plural ending -s occurs with nouns of all three genders, but it is
restricted to some special cases.
(a) – s is used with many loan-words from English or French
das Atelier – die Ateliers / der Balkon – die Balkons / der Chef – die
Chefs / das Detail – die Details / der Download – die Downloads / das Hotel
– die Hotels / das Labor – die Labors / der Park – die Parks / der Scheck –
die Schecks / der Streik – die Streiks / das Team – die Teams / der Waggon –
die Waggons
Some loan-words from English and French have been assimilated and have German plural forms. This is especially the case
with English nouns in -el and -er, which almost always have the
regular endingless plural, e.g. der Tunnel – die Tunnel; der Computer
– die Computer, although there can be some variation, and forms with -
s (e.g. die Tunnels) occur occasionally.
Some loans from French like
der Balkon tend to have the plural in -s if they are given a French
pronunciation, i.e. [balkɔ˜], but a German plural, i.e. die Balkone if
they are pronounced in a German fashion, i.e. [balko:n]. In writing,
though, die Balkone is nowadays more frequent.
English loan-words in -y have a plural in -ys, e.g. die Babys, die
Handys, die Partys, not in -ies like English babies, etc.
(b) – s is used with most words ending in a vowel other than
unstressed -e
das Auto – die Autos der Euro – die Euros das Genie – die Genies die
Oma – die Omas der Ossi – die Ossis der Uhu – die Uhus
Some foreign words with unusual plurals are exceptions to this rule (see 1.2.5), as
are most feminine nouns in -ee and -ie which have regular plurals,
e.g. die Allee – die Alleen, die Galerie – die Galerien.
(c) – s is used with abbreviations and shortened words
die AG – die AGs der PKW – die PKWs der Akku – die Akkus die Lok – die
Loks
This ending is often omitted with some abbreviations, especially
die LKW, die PKW.
(d) – s is used with some North German seafaring words
The most frequent are:
das Deck – die Decks das Dock – die Docks der Kai – die Kais das Wrack
– die Wracks (e) - s is used in colloquial speech with some words
referring to persons
die Bengels, die Doktors, die Fräuleins, die Jungs (older: die
Jungens),
die Kerls, die Kumpels, die Mädels, die Onkels
This usage is typical of non-standard North German speech, where some
of them are very frequent. The standard plural form (die Jungen, die
Kumpel, die Mädel, etc.) is preferred in writing.
(f) – s is used with family and other names
die Müllers, die Buddenbrooks, zwischen den beiden Deutschlands (Zeit)
With geographical names it is also possible to use an endingless
plural, e.g. die beiden Korea(s).
1.2.5 Unusual plurals
A number of words, particularly those borrowed into German from the
classical languages or Italian, have kept unusual plural forms. Some
are in practice restricted to formal written language.
(a) Most words in -us or -um replace this by -en in the plural
das Album – die Alben (coll. Albums) / der Genius – die Genien / der
Globus – die Globen (rarely: die Globusse) / das Museum – die Museen / der
Organismus – die Organismen / der Rhythmus – die Rhythmen / das Zentrum –
die Zentren / der Zyklus – die Zyklen
Some foreign words in -us have
adopted a native plural in -e (spelled with double -ss-):
der Bonus – die Bonusse (also die Boni) / der Bus – die Busse / der Krokus
– die Krokusse (rarely: die Krokus) / der Zirkus – die Zirkusse
There are a few irregularities and exceptional cases:
der ʹKaktus – die Kakʹteen, pronounced [kakte:ən] (coll. die Kaktusse)
das Tempus tense – die Tempora
der Terminus term – die Termini
das Visum – die Visa (die Visen)
From: Martin Durrell: "Hammer's German Grammar and Usage", Routledge: New York, 62017.
Since I have never heard ETF before, my instinct would say that the plural ETFs is acceptable. German Wikipedia is doing likewise:
Der Rückgang war auf die Kursverfälle im Zuge der Finanzkrise zurückzuführen, netto verzeichneten ETFs auch 2008 einen Zufluss an Mitteln.
It might be argued that adding -s is the default mode for newly created and imported words, so using it is in a way the safest choice:
(From Peter Gallmann: Pluralformen, Jena Sommersemester 2016 )
- The s in AIDS or SARS stands for syndrome, that has a perfectly regular plural "syndromes"; but what is the correct plural for the acronym SARS?
