Babel and csquotes Language Problem in Biblatex

Question

I have spent a lot of time customizing the biblatex style to my needs. Just when I thought it's finally ready, I can't seem to work biblatex properly.

I need to use babel for correct hyphenation. But Turkish language is not available in csquotes. This causes errors and I can't compile my document. I can only compile it if I disable babel. Here are the codes,

\documentclass[11pt,a4paper,oneside]{article}
    \usepackage[turkish]{babel}
    \usepackage[utf8]{inputenc}
    \usepackage[T1]{fontenc}
    \usepackage[a4paper, top=2.5cm, right=2.5cm, bottom=2.5cm, left=4cm]{geometry}
    \usepackage{setspace}
    \usepackage[backend=biber, style=authoryear,date=year, firstinits=true, natbib=true]{biblatex}
    \usepackage{csquotes}

And here is the error log:

Errors:

./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing number, treated as zero. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing number, treated as zero. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing number, treated as zero. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Extra \endcsname. [...lmektedir \citep{frankel1981,diamond1984}.]
./test.tex:46: Missing \endcsname inserted. [...ya olduğu bilinmektedir \citep{albayrak} ]
./test.tex:46: Extra \endcsname. [...ya olduğu bilinmektedir \citep{albayrak} ]
./test.tex:46: Missing \endcsname inserted. [...ya olduğu bilinmektedir \citep{albayrak} ]
./test.tex:46: Extra \endcsname. [...ya olduğu bilinmektedir \citep{albayrak} ]
./test.tex:46: Missing number, treated as zero. [...ya olduğu bilinmektedir \citep{albayrak} ]
./test.tex:46: Missing \endcsname inserted. [...ya olduğu bilinmektedir \citep{albayrak} ]
./test.tex:46: Extra \endcsname. [...ya olduğu bilinmektedir \citep{albayrak} ]
./test.tex:46: Missing \endcsname inserted. [...ya olduğu bilinmektedir \citep{albayrak} ]
./test.tex:46: Extra \endcsname. [...ya olduğu bilinmektedir \citep{albayrak} ]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing number, treated as zero. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing number, treated as zero. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing number, treated as zero. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Use of \\blx@imc@bibstring doesn't match its definition. [\end]
./test.tex:64: Extra }, or forgotten \endgroup. [\end]
./test.tex:64: Argument of \@gobble has an extra }. [\end]
./test.tex:64: Paragraph ended before \@gobble was complete. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing number, treated as zero. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing number, treated as zero. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]
./test.tex:64: Missing \endcsname inserted. [\end]
./test.tex:64: Extra \endcsname. [\end]

Warnings:

./test.tex: Package biblatex Warning: Conflicting options.
./test.tex: Package csquotes Warning: No style for language 'turkish'.

Is there any way to workaround this?

Here is a MWE. Document compiles fine if babel is disabled :

\documentclass[11pt,a4paper,oneside]{article}
    \usepackage[turkish]{babel}
    \usepackage[utf8]{inputenc}
    \usepackage[T1]{fontenc}
    \usepackage[a4paper, top=2.5cm, right=2.5cm, bottom=2.5cm, left=4cm]{geometry}
    \usepackage[backend=biber, style=authoryear, date=year, firstinits=true, natbib=true]{biblatex}
    \usepackage{csquotes}
    \usepackage{filecontents}   

\begin{filecontents*}{\jobname.bib}
  @book{Knu86,
    author = {Knuth, Donald E.},
    year = {1986},
    title = {The \TeX book},
  }
\end{filecontents*}


\addbibresource{\jobname.bib}


\begin{document}

\section{mwe}
{
 Lorem ipsum dolor sit amet, consectetur adipiscing elit \cite{Knu86}. Vivamus a fermentum tortor. Curabitur lacinia feugiat eros. Aenean sagittis pulvinar orci id sodales. Aenean vulputate leo elit, vitae euismod odio cursus sed. Integer nec risus semper, lobortis arcu nec, sodales urna. Sed convallis vitae justo nec vehicula. Maecenas eleifend, erat sit amet ultricies ultricies, mi nibh hendrerit arcu, in consequat leo dui vitae eros.  
}

%KAYNAKÇA
\printbibliography
\end{document}

Answer 1

The babel module for Turkish defines = as a shorthand that is aimed to leave some space before it in case it's used in text.

Since there is no reason for using = in text, just remove it from the shorthand list:

\usepackage[turkish,shorthands=:!]{babel}

if you have babel version 3.9

\documentclass[11pt,a4paper,oneside]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[turkish,shorthands=:!]{babel}

\usepackage[
  a4paper,
  top=2.5cm,
  right=2.5cm,
  bottom=2.5cm,
  left=4cm,
]{geometry}

\usepackage{csquotes}
\usepackage[
  backend=biber,
  style=authoryear,
  date=year,
  firstinits=true,
  natbib=true,
]{biblatex}

A different workaround, if you still have an old version of babel is to load it after biblatex

\documentclass[11pt,a4paper,oneside]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\usepackage[
  a4paper,
  top=2.5cm,
  right=2.5cm,
  bottom=2.5cm,
  left=4cm,
]{geometry}

\usepackage{csquotes}
\usepackage[
  backend=biber,
  style=authoryear,
  date=year,
  firstinits=true,
  natbib=true,
]{biblatex}

\usepackage[turkish]{babel}