getting colons after every description item (not using listing package)

Question

current output:

Desc 1 Bla 1

wanted output:

Desc 1: Bla 1

---

MWEs:

current output:

\documentclass[oneside,12pt]{scrartcl}
\usepackage{polyglossia}
\setdefaultlanguage{german}
\usepackage{fontspec}
\begin{document}
\begin{description}
\item[Desc 1] Bla 1
\end{description}
\end{document}

wanted output:

\documentclass[oneside,12pt]{scrartcl}
\usepackage{polyglossia}
\setdefaultlanguage{german}
\usepackage{fontspec}
\begin{document}
\begin{description}
\item[Desc 1:] Bla 1
\end{description}
\end{document}

of course I know I could do it by regex replace... but i'm pretty sure there is an easier and more elegant way. and also i'm looking for a solution for the case where i have >100 items

Answer 1

Redefine \descriptionlabel to add the colon:

\documentclass[oneside,12pt]{scrartcl}
\usepackage{polyglossia}
\setdefaultlanguage{german}
\usepackage{fontspec}

\renewcommand*{\descriptionlabel}[1]{\hspace{\labelsep}\descfont #1:}

\begin{document}
\begin{description}
\item[Desc 1] Bla 1
\item[Desc 2] Bla 2
\item[Desc 3] Bla 3
\end{description}
\end{document}

The result:

I didn't make any prevision in the case in which the optional argument of \item isn't used, since this wouldn't make sense in the first place in a description.

Answer 2

This redefines \item, but will give default behavior (omit the colon) when no optional argument is specified.

\documentclass[oneside,12pt]{scrartcl}
%\usepackage{polyglossia}
%\setdefaultlanguage{german}
%\usepackage{fontspec}
\let\svitem\item
\renewcommand\item[1][\relax]{\ifx\relax#1\svitem\else\svitem[#1:]\fi}
\begin{document}
\begin{description}
\item[Desc 1] Bla 1
\item Default empty tag
\end{description}
\end{document}

Because it redefines \item, the above MWE will affect other list types. However, that can be avoided with the following MWE, which will only affect the description environment.

\documentclass[oneside,12pt]{scrartcl}
%\usepackage{polyglossia}
%\setdefaultlanguage{german}
%\usepackage{fontspec}
\let\svitem\item
\newcommand\altitem[1][\relax]{\ifx\relax#1\svitem\else\svitem[#1:]\fi}
\let\svdescription\description
\def\description{\let\item\altitem\svdescription}
\begin{document}
\begin{description}
\item[Desc 1] Bla 1
\item Default empty tag
\end{description}
\begin{itemize}
\item[Desc 1] Bla 1
\item Default empty tag
\end{itemize}
\end{document}