Issue using babel package to change language

I am writing my masters thesis. It is mandatory to include an abstract in the language of my own country. In my case this is dutch. I have tried doing this with the babel package found at https://www.ctan.org/pkg/babel.

However, the language change does not take effect while making use if the SphdThesis as document class. I have successfully made use of the babel package using the article as document class.

Does anyone know why the babel package does not take effect?

Down below the .tex file of my document is stated. Also my separate abstract.tex document is included.

Thesis.tex

\documentclass{SPhdThesis}

% PDF and title properties.
\SgSetTitle{}
\SgSetAuthor{}
\SgSetAuthorDegrees{}
\SgSetYear{}
\SgSetDegree{}
\SgSetDepartment{}
\SgSetUniversity{}
\SgSetDeclarationDate{\today}

% Packages
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[dutch,english]{babel}
\usepackage{geometry}
\geometry{left=1.0in, right=1.0in}
\usepackage{apacite}
\usepackage{natbib}
\usepackage[section]{placeins}
\usepackage{graphicx}
\usepackage{caption}
\usepackage{subfig}
\usepackage{tabularx}
\usepackage{verbatim}
\usepackage{lscape}
\usepackage{tikz}
\usepackage{tablefootnote}
\usepackage[toc,page]{appendix}
\usepackage[nokeyprefix]{refstyle}
\usepackage{datetime}
\usepackage{algorithm2e}
\usepackage{algorithm}
\usepackage{algpseudocode}% http://ctan.org/pkg/algorithmicx
\usepackage[refpage]{nomencl}
\usepackage{wrapfig}
\usepackage{adjustbox}
\usepackage{pdflscape}
\usepackage{lscape}

\bibliographystyle{apacite}
\setcitestyle{authoryear,open={(},close={)}}

\newenvironment{conditions}
  {\par\vspace{\abovedisplayskip}\noindent\begin{tabular}{>{$}l<{$} @{${}={}$} l}}
  {\end{tabular}\par\vspace{\belowdisplayskip}}

\makenomenclature
\setcounter{tocdepth}{3}
\setcounter{secnumdepth}{2}
\setlength{\headheight}{30pt}

% The document.
\begin{document}
        \input{titlepage.tex}
        \SgAddToc % Table of contents.
        \input{abstract.tex}
        \input{samenvatting.tex}
        %\SgAddLof%  List of figures.
        %\SgAddLot%  List of tables.
        %\SgAddLoa%  List of algorithms.
        \input{introduction}
        \input{methods.tex}
        \input{results.tex}
        \input{discussion}
        \input{conclusion}
        \SgIncludeBib{mendeley}
        \input{nomenclature.tex}
        \printnomenclature
        \input{appendix}
\end{document}

(abstract in own language) Samenvatting.tex

%\begin{otherlanguage}{dutch}
\selectlanguage{dutch}
\begin{abstract}

\end{abstract}
%\end{otherlanguage}

saurabhg17 / SPhdThesis

Issue using babel package to change language #7