\documentclass[british]{article}
\usepackage{babel}
\usepackage[bibstyle=standard,date=long,abbreviate=false]{biblatex}
\addbibresource{\jobname.bib}
\begin{filecontents}{\jobname.bib}
@inproceedings{dateTest,
date={2014-11/2015-04-26},
author={JB},
translator={JW and AB and PLK},
title={is the date \emph{long} as seen in the manual?},
}
\end{filecontents}
\begin{document}
\fullcite{dateTest}
\end{document}