Can't change name of Abstract while using Babel

Question

I am writing a thesis and I want to have two abstracts in different languages, English and Catalan. I started with a thesis template from my university (only in English) and then added the Babel package. I can successfully create two abstracts in different languages, but I'm not managing to change the name of the second Abstract to "Resum". Found online that Babel changes renewcommand so this is the solution for most people:

\addto{\captionscatalan}{\renewcommand{\abstractname}{Resum}}

This does not work for me, though, as the second one still appears as "Abstract". This is how I defined them:

\documentclass[a4paper, oneside]{discothesis}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[english,catalan]{babel} 
\begin{document}

%Abstract in English
\begin{abstract}
Abstract
\end{abstract}

%Abstract in Catalan
\begin{abstract}
\selectlanguage{catalan}
\addto{\captionscatalan}{\renewcommand{\abstractname}{Resum}}
Resum
\end{abstract}
\selectlanguage{english}

\end{document}

Also tried defining my own environment and got exactly the same result:

\documentclass[a4paper, oneside]{discothesis}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[english,catalan]{babel} 
\newenvironment{poliabstract}[1]
  {\renewcommand{\abstractname}{#1}\begin{abstract}}
  {\end{abstract}}
\begin{document}

\selectlanguage{english}
\begin{poliabstract}{Abstract} 
Abstract in english
\end{poliabstract}

\selectlanguage{catalan}
\begin{poliabstract}{Resum}
Resum en català
\end{poliabstract}

\selectlanguage{english}

\end{document}

The abstract is defined in this way in the cls file, haven't touched anything from the template file:

    \newenvironment{abstract}
    {\chapter*{Abstract}}
    {\vfill                 %kai
    \noindent               %kai
    \ifx \@keywords \@empty
        \relax
    \else
        {\bf Keywords:} \@keywords \\[6pt] %tobias
    \fi
% 
    \ifx \@categories \@empty
        \relax
    \else
        {\bf CR Categories:} \@categories   %tobias
    \fi

    \addcontentsline{toc}{chapter}{Abstract}
    }

Answer 1

The name ‘Abstract’ is hardcoded in the (somewhat buggy) class. So you must redefine abstract, as suggested before. The following works for me, and it’s (imo) the canonical way the use two abstracts (I’m assuming Catalan is the main language):

\documentclass[a4paper, oneside]{discothesis}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[english,catalan]{babel} 

\makeatletter
\renewenvironment{abstract}
  {\chapter*{\abstractname}}
  {\vfill               %kai
  \noindent             %kai
  \ifx \@keywords \@empty
    \relax
  \else
    {\bf Keywords:} \@keywords \\[6pt] %tobias
  \fi
  \ifx \@categories \@empty
    \relax
  \else
    {\bf CR Categories:} \@categories   %tobias
  \fi
  \addcontentsline{toc}{chapter}{\abstractname}}
\makeatother

\begin{document}

\begin{otherlanguage}{english}
\begin{abstract}
Abstract
\end{abstract}
\end{otherlanguage}

\begin{abstract}
Resum
\end{abstract}

\end{document}

If the main language is English, reverse the order of languages (ie, catalan,english), and change the abstracts to:

\begin{abstract}
Abstract
\end{abstract}

\begin{otherlanguage}{catalan}
\begin{abstract}
Resum
\end{abstract}
\end{otherlanguage}

If you find further issues (for example, ‘Keywords’ is hardcoded, too), please extend your MWE.

Answer 2

The definition of the abstract from your template is a little bit strange. But since you're more or less bound to the template, here's my simple and fast solution.

Just redefine the environment, using xparse and its check mechanisms for optional arguments, the following way in the praeambel:

\makeatletter
\RenewDocumentEnvironment{abstract}{o}{%
    \chapter*{\abstractname}%
    \IfValueT{#1}{\begin{otherlanguage}{#1}}%
}{%
    \vfill                 %kai
    \noindent               %kai
    \ifx \@keywords \@empty
        \relax
    \else
        {\bf Keywords:} \@keywords \\[6pt] %tobias
    \fi
% 
    \ifx \@categories \@empty
        \relax
    \else
        {\bf CR Categories:} \@categories   %tobias
    \fi
    \addcontentsline{toc}{chapter}{\abstractname}%
    \IfValueT{#1}{\end{otherlanguage}}%
}
\makeatother

Now you can use it the following way:

\begin{abstract}[<language-option>]
Text...
\end{abstract}

If the optional argument is left away, you use the main language of your document.

And you still can use the \addto{\captionscatalan}{\renewcommand{\abstractname}{Resum}} command, which is the recommended way with babel.