Bicaption with multiline hanging caption and extra space

Question

I am using the bicaption package with the following style and I encountered a problem with the option format. Does someone know how to get a good way to proceed?

The current format looks like:

Bild 1.1:|--x--|Unterschrift
Fig 1.1: |--x--|caption

The extra distance |--x--| is managed by format= X.Xcm within the bicaption options. It works quite nicely. But when I am using a very long, in fact douple line caption I encountered a case like:

Bild 1.1:|--x--|Unterschrift...
sehr lang
Fig 1.1: |--x--|very long...
caption

I wanted to change this to

Bild 1.1:|--x--|Unterschrift...
                sehr lang
Fig 1.1: |--x--|very long...
                caption

This means a hanging format. But when I change format=hang of course the extra distance is gone an it will look like this:

Bild 1.1: Unterschrift...
          sehr lang
Fig 1.1:  very long...
          caption

Thank for any idea how to combine the two things!

Here is a MWE:

\documentclass[12pt,BCOR0pt,DIV12]{scrartcl}
\usepackage[utf8]{inputenc}
\usepackage[german]{babel}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{lipsum}
\usepackage{graphicx}
\usepackage[labelfont=it, skip=-12pt, justification=raggedright,singlelinecheck=false, margin={2mm,0mm},hang]{caption}
\usepackage[labelfont=it, skip=-12pt, justification=raggedright,singlelinecheck=false, margin={2mm,0mm}]{bicaption}
\captionsetup[figure][bi]{labelfont=it, justification=raggedright, singlelinecheck=false, margin={0mm,0mm}}
\addto\captionsngerman{\renewcommand\figurename{Test}}
\captionsetup[figure][bi-first]{name=Test}
\captionsetup[figure][bi-second]{name=Fig.}
\numberwithin{figure}{section}
\DeclareCaptionFormat{4.0cm}{\hbox to 4.0cm{#1#2\hfill}#3\par}
\captionsetup[figure][bi]{format=4.0cm}

\begin{document}

\lipsum[1]

\begin{figure}[h!]
  \includegraphics[draft,width=\textwidth]{Beispiel}
  \captionsetup{skip=0pt}
  \bicaption[indention=0pt]{Dies ist eine sehr lange Unterschrift in zwei Sprachen die über eine Zeile hinaus geht}{This is supposed to be a very long multiline caption in two languages}  
  \label{fig:Beispiel}
\end{figure}

\lipsum[2]

\end{document}

Answer 1

A \parbox around the caption text might do the trick:

\documentclass[12pt,BCOR0pt,DIV12]{scrartcl}
\usepackage[utf8]{inputenc}
\usepackage[german]{babel}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{lipsum}
\usepackage{graphicx}
\usepackage[labelfont=it, skip=-12pt, justification=raggedright,singlelinecheck=false, margin={2mm,0mm},hang]{caption}
\usepackage[labelfont=it, skip=-12pt, justification=raggedright,singlelinecheck=false, margin={2mm,0mm}]{bicaption}
\captionsetup[figure][bi]{labelfont=it, justification=raggedright, singlelinecheck=false, margin={0mm,0mm}}
\addto\captionsngerman{\renewcommand\figurename{Test}}
\captionsetup[figure][bi-first]{name=Test}
\captionsetup[figure][bi-second]{name=Fig.}
\numberwithin{figure}{section}
\DeclareCaptionFormat{4.0cm}{\hbox to 4.0cm{#1#2\hfill}\parbox[t]{\dimexpr\linewidth-4cm\relax}{#3}\par}
\captionsetup[figure][bi]{format=4.0cm}

\begin{document}

\lipsum[1]

\begin{figure}[h!]
  \includegraphics[draft,width=\textwidth]{example-image}
  \captionsetup{skip=0pt}
  \bicaption[indention=0pt]{Dies ist eine sehr lange Unterschrift in zwei Sprachen die über eine Zeile hinaus geht}{This is supposed to be a very long multiline caption in two languages}  
  \label{fig:Beispiel}
\end{figure}

\lipsum[2]

\end{document}