Sort test for https://tex.stackexchange.com/q/396126/35864

danishsort.tex

\documentclass{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[danish]{babel}
\usepackage{csquotes}
\usepackage[style=authoryear, backend=biber]{biblatex}

\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@online{aal,
  author = {Aal},
  title  = {aal},
  year  = {2016},
}
@online{aam,
  author = {Åm},
  title  = {åm},
  year   = {2016},
}
@online{aak, 
  author = {Åk},
  title  = {åk},
  year   = {2016},
}
@online{ab,
  author = {Abba},
  title  = {abba},
  year   = {2016},
}
@online{oel,
  author = {Øl},
  title  = {øl},
  year   = {2016},
}
@online{onno,
  author = {Onno},
  title  = {onno},
  year   = {2016},
}
@online{aer,
  author = {Ær},
  title  = {ær},
  year   = {2016},
}
@online{ea,
  author = {Ea},
  title  = {ea},
  year   = {2016},
}
@online{ez,
  author = {Ez},
  title  = {ez},
  year   = {2016},
}
@online{fa,
  author = {Fa},
  title  = {fa},
  year   = {2016},
}
@online{fu,
  author = {Fu},
  title  = {fu},
  year   = {2016},
}
\end{filecontents*}

\addbibresource{\jobname.bib}
\addbibresource{biblatex-examples.bib}
\begin{document}

\nocite{aksin,ab,aak,aam,aal,cicero,worman,oel,sigfridsson,onno,aer,doody,gillies,hammond,itzhaki,kowalik,loh,malinowski,nietzsche:ksa1,piccato,reese,ea,ez,fu,fa}
\printbibliography
\end{document}

output-biber27-miktex.png