documentclass{scrreprt}
usepackage[main=ngerman, english]{babel}
usepackage[babel, german=quotes]{csquotes}
usepackage[ngerman]{isodate}
usepackage[ngerman]{datetime}
%----------------------------------------------------------------------------
%   BIB
%----------------------------------------------------------------------------
 usepackage[
    backend=biber,
    style=authoryear,
    sorting=nyvt,
    maxnames=25,
    dashed=false,
    isbn=false
  ]{biblatex}
 addbibresource{library.bib}
renewcommand{mkbibnamefamily}[1]{textsc{#1}}
renewcommand{labelnamepunct}{addcolonspace}
DeclareFieldFormat{postnote}{#1}
DeclareFieldFormat{multipostnote}{#1}
renewcommandpostnotedelim{addcolonaddspace}
DeclareFieldFormat
  [article,inbook,incollection,inproceedings,patent,unpublished]
  {title}{#1isdot}
DeclareFieldFormat
  [thesis]
  {title}{mkbibemph{#1}isdot}  % thesis title italic


% no period after addon titles
usepackage{xpatch}
DeclareFieldFormat{titleaddon}{mkbibbrackets{#1}}
DeclareDelimFormat{titleaddondelim}{addspace}
xpatchbibmacro{title}
  {printfield{titleaddon}}
  {setunit{printdelim{titleaddondelim}}%
   printfield{titleaddon}}
  {}
  {}
DeclareFieldFormat{booktitleaddon}{mkbibbrackets{#1}}
DeclareDelimFormat{booktitleaddondelim}{addspace}
xpatchbibmacro{booktitle}
  {printfield{booktitleaddon}}
  {setunit{printdelim{titleaddondelim}}%
   printfield{booktitleaddon}}
  {}
  {}
DeclareFieldFormat{maintitleaddon}{mkbibbrackets{#1}}
DeclareDelimFormat{maintitleaddondelim}{addspace}
xpatchbibmacro{maintitle}
  {printfield{maintitleaddon}}
  {setunit{printdelim{titleaddondelim}}%
   printfield{maintitleaddon}}
  {}
  {}

begin{document}
nocite{*}
printbibliography[heading=bibintoc,title={Literaturverzeichnis}]
end{document}

@article{yomiuri.1981,
 journal = {Yomiuri Shimbun},
 type = {newspaper},
 year = {22.01.1981},
 pages = {20},
 location = {Kanagawa},
 note = {Morgenausgabe},
 title = {Atarashī taishū bunka sanmi ittai no dendō. Kawasaki ni manga shashin eizō bunka sentā},
 titleaddon = {Neuer Palast der Dreifaltigkeit der Populärkultur. Das Zentrum für Manga, Fotografie und visuelle Kultur in Kawasaki}
}

@article{testauthor.1981,
 journal = {Yomiuri Shimbun},
 author = {Test, Author},
 type = {newspaper},
 year = {22.01.1981},
 pages = {20},
 location = {Kanagawa},
 note = {Morgenausgabe},
 title = {Atarashī taishū bunka sanmi ittai no dendō. Kawasaki ni manga shashin eizō bunka sentā},
 titleaddon = {Neuer Palast der Dreifaltigkeit der Populärkultur. Das Zentrum für Manga, Fotografie und visuelle Kultur in Kawasaki}
}