documentclass{scrreprt}
KOMAoptions{toc=chapterentrydotfill}
renewcommand{contentsname}{Inhaltsverzeichnis}
usepackage[printonlyused]{acronym} %does this even make sense with glossaries-extra?
usepackage[record,style=indexgroup,nomain]{glossaries-extra}

newglossary*{acronym}{Akronymverzeichnis}
newglossary*{japanese}{Japanisch Deutsch}
newglossary*{german}{Deutsch Japanisch}

glsnoexpandfields

newcommand*{germanlettergroup}[1]{#1}

GlsXtrLoadResources[
  src=glossary,
  sort={de-DE},
  dual-sort={de-DE},
  type=japanese,
  dual-type=german,
  dual-prefix={de.}
]

begin{document}
tableofcontents
setcounter{page}{2}
Japanese: gls{taikareform}
gls{http}
German: gls{de.taikareform}
printunsrtglossaries
end{document}

@dualentry{taikareform,
 name={taika no kaishin},
 description={Taika-Reform(en)}
 }

 @acronym{http,
  short = {HTTP},
  long = {Hypertext Transfer Protocol}
}