How do I properly cite this German-language paper?

Question

I am currently converting a bibliography for a paper (which I did not write) into bibtex and I am having trouble understanding the citations in the image below: (these are not my own, this is just an example how other authors cited the papers I am interested in)

I do not have very much experience with German-language publications, and I've been told that they have some special rules associated with them such that that nouns should always be capitalized, but I can't find a source that provides a lot of detail.

What is the meaning of the two dates in citations such as this (I've also seen some with two sets of page numbers) and how should I put it into a bibtex entry? This is what I was given:

\bibitem[Cig98]{Cig98} J. Cigler, 
Operatormethoden f\"ur $q$-Identitäten. VI. Geordnete Wurzelb\"aume und $q$
Catalan-Zahlen,
\"Osterreich. Akad. Wiss. Math.-Natur. Kl. Sitzungsber. II 206 (1997), 253
-266 (1998).

and this is what I've changed it to so far

@article{Cig98,
Author = {J.~ Cigler},
Journal = {\"Osterreich. Akad. Wiss. Math.-Natur. Kl. Sitzungsber. II},
Title = {{O}peratormethoden f\"ur $q$-{I}dentit\"aten.~ {VI}.~ {G}eordnete {W}urzelb\"aume und $q$-{C}atalan-{Z}ahlen}},
Year = {1997},
Volume = {206},
Pages = {253--266}

Is this okay so far? How do I finish properly entering this citation?

Answer 1

I'd say that "1997" is the year, "206" is the volume number, and "1996" is the issue number. I'd keep the abbreviated journal name, as I see little point in writing the full form, which would be "{\"O}sterreichische Akademie der Wissenschaften, Mathematisch-Naturwissenschaftliche Klasse, Sitzungsbericht~II".

\RequirePackage{filecontents}
\begin{filecontents}{mybib.bib}
@article{Cig97a,
  author  = "J. Cigler",
  journal = "{\"O}ster\-reich.\ Akad.\ Wiss.\ Math.-Natur.\ Kl.\ Sitzungsber.~II",
  title   = "{Operatormethoden f{\"u}r $q$-{I}dentit{\"a}ten. 
             IV\@.~Eine Klasse von $q$-Gould-Polynomen}",
  year    = 1997,
  volume  = 206,
  number  = 1996,
  pages   = "169-174",
}
@article{Cig97b,
  author  = "J. Cigler",
  journal = "{\"O}ster\-reich.\ Akad.\ Wiss.\ Math.-Natur.\ Kl.\ Sitzungsber.~II",
  title   = "{Operatormethoden f{\"u}r $q$-{I}dentit{\"a}ten.
            V\@.~$q$-Catalan B{\"a}ume}",
  year    = 1997,
  volume  = 206,
  number  = 1996,
  pages   = "175-182",
}

\end{filecontents}
\documentclass{article}
\usepackage[numbers]{natbib}
\bibliographystyle{plainnat}
\begin{document}
\nocite{*}
\bibliography{mybib}
\end{document}