acro: move translation to the next line for selected acronyms only

In case you should want to use version 3 here is how you then could define a boolean property for acronyms which you could test in a list template and depending on its value insert a linebreak or not. Such a property is defined with

DeclareAcroProperty?{boolean-property}

and checked in a template with

acroifbooleanTF{boolean-property}{true}{false}

The following example calls it foreign-newline and shows a template similar to the predefined description template (I left the extra and pages fields away but they could be added, of course):

documentclass{article}
usepackage[T1]{fontenc}
usepackage{lmodern}
usepackage[english,ngerman]{babel}
usepackage{acro}
usepackage{enumitem}

DeclareAcroProperty?{foreign-newline}

NewAcroTemplate[list]{custom}{
  acroheading
  acropreamble
  begin{description}[
    labelwidth = 3em ,
    leftmargin = 3.5em ,
    noitemsep ,
    itemindent = 0pt]
    acronymsmapF{%
      item[acrowrite{short}acroifT{alt}{/}acrowrite{alt}:]%
        acrowrite{list}%
        acroifT{foreign}{%
          acroifbooleanTF{foreign-newline}{newline}{ }%
          (textit{acrowrite{foreign}})
        }%
    }
    { item AcroRerun }%
  end{description}%
}

acsetup{
  list/template = custom
}

DeclareAcronym{Rv}{
  short = Rv ,
  long = Fluss ,
  foreign = river ,
  foreign-babel = english
}
DeclareAcronym{Drs}{
  short = Drs ,
  long = Donaudampfschiff ,
  foreign = Donau river steamer ,
  foreign-babel = english ,
  foreign-newline = true
}

begin{document}

twocolumn

acuseall

printacronyms

end{document}