begin{filecontents}{myveryown.bbx}
ProvidesFile{myveryown.bbx}[2018/04/24 v1.0 biblatex bibliography style]
RequireBibliographyStyle{authortitle}
DeclareLanguageMapping{ngerman}{ngerman-myveryown}
end{filecontents}
begin{filecontents}{ngerman-myveryown.lbx}
ProvidesFile{ngerman-myveryown.lbx}[2018/04/24 v1.0 biblatex localization]
InheritBibliographyExtras{ngerman}
DeclareBibliographyStrings{%
   byeditor = {{herausgegeben von}{hggadddotspace vadddot}},
}
end{filecontents}
begin{filecontents}{abibfile.bib}
@book{akey,
address = {Zürich and Wiesbaden},
edition = {My very own edition},
title = {A very long title},
volume = {1},
publisher = {My publisher},
author = {Author, An},
year = {1999},
}
end{filecontents}
documentclass{book}
usepackage[utf8]{inputenc}
usepackage[T1]{fontenc}
usepackage[ngerman]{babel}
usepackage[bibstyle=myveryown]{biblatex}
addbibresource{abibfile.bib}
begin{document}
Testnocite{*}
printbibliography
end{document}

ProvidesFile{ngerman-myveryown.lbx}[2018/04/24 v1.0 biblatex localization]
InheritBibliographyExtras{ngerman}
DeclareBibliographyStrings{%
   inherit  = {ngerman},
   byeditor = {{herausgegeben von}{hggadddotspace vadddot}},
}