Vjylku

i uses count function instead of showing "ı" character.
Tried i, {i} $$i$$, imath text{i} but continues to count.

documentclass[12pt, letterpaper, oneside]{article}



usepackage[T1]{fontenc}

usepackage[turkish]{babel}

usepackage[utf8]{inputenc}

usepackage{datetime}

usepackage{amsmath}

usepackage{fancyhdr}

usepackage{graphicx}

usepackage[colorinlistoftodos]{todonotes}

usepackage{tabularx}

usepackage{url}

usepackage{booktabs}

usepackage{titlesec}

usepackage{float}

usepackage{hyperref}

usepackage{hypcap}

usepackage{apacite}

usepackage{needspace} %sayfa sonu boşluklarını ayarlamak için

usepackage[section]{placeins} 

usepackage{xcolor}

hypersetup{                    

    colorlinks,

    linkcolor={red!50!black},

    citecolor={blue!50!black},

    urlcolor={blue!80!black}

}

bibliographystyle{apacite}  

usepackage{fancyref}

usepackage{tikz}

usetikzlibrary{babel}

usepackage{pgf-pie} %piechart için

usepackage{subcaption}

usepackage{pgfplots}

usepackage{longtable}

usepackage{makecell}

usepackage{booktabs}

usepackage{lscape}



usepackage[font={footnotesize}]{caption}

newcommand{sekil}[1]{(Şekil ref{fig:#1})}

newcommand{tablo}[1]{(Tablo ref{tab:#1})}

newcommand{HRule}{rule{linewidth}{0.5mm}}

usepackage{lmodern}

usepackage{etoolbox}

AtBeginEnvironment{tikzpicture}{shorthandoff{;}}



%---------------------- Header -------------------------------%

fancyhead[L]{R. Özgür ALTUN}

fancyhead[R]{Tangonun Sosyal Dansçıları}

fancyhead[C]{}

fancyfoot[C]{thepage}  

pagestyle{fancy}

setlength{headheight}{26pt}





begin{document}

begin{figure}[htb!]

begin{center}

begin{tikzpicture}[scale = 0.9]

inputencoding{utf8}

usetikzlibrary{babel}

    pie[sum=auto, text=legend, color={black!0, black!10, black!30, black!50, black!80}, explode=0.1, scale font, before number= {%}]{9/Doğru veya yanliş olduğunu umursamadan keyif almak, 11/Çalişilan bir eş ile yapmak, 26/Hatali da olsa akici{i}   yapmak, 2/Keyif almak, 51/Mükemmel şekilde yapana kadar tekrar etmiş olmak}

end{tikzpicture}

caption{Yeni figür uygulanmasında öncelikli tercih.}   

label{fig:yenifiguroncelik}

end{center}

end{figure}



end{document}

I'm afraid there's little to do. The package pgf-pie is very badly written.

While in a user document one can choose to use i inside a foreach cycle, this should not be inflicted to the users of a package, which should be as neutral as possible.

Ask the developers to change the local variables in their foreach cycles.

In the meantime, add

lettikzi=i % Fix for bad programming in pgf-pie

to your document preamble, just before begin{document}, and in the text for a pie chart use tikzi where i should be used. No direct UTF-8 input, but the explicit command tikzi.

begin{tikzpicture}[scale = 0.9]

  pie[

    sum=auto,

    text=legend,

    color={black!0, black!10, black!30, black!50, black!80},

    explode=0.1,

    scale font,

    before number= {%}

  ]{%

    9/Doğru veya yanliş olduğunu umursamadan keyif almak,

    11/Çalişilan bir eş ile yapmak,

    26/Hatali da olsa akicitikzi{} yapmak,

    2/Keyif almak,

    51/Mükemmel şekilde yapana kadar tekrar etmiş olmak

}

end{tikzpicture}

Found an easy solution at second hour of searching. symbol{25} worked for me.