plk
Turkish: A dot over a capital I disappeared between TeX Live 2021-22
In this example, you can "İçinde" in TeX Live 2021, but "Içinde" in recent TeX Live 2022, tested on Overleaf (LaTeX2e <2022-06-01> patch level 5, L3 programming layer <2022-08-05>). From my understanding, the first option is correct, so this is a newly created bug.
MWE:
\documentclass[a4paper]{article}
\begin{filecontents}{biblio.bib}
@incollection{Doe,
author = {Doe, John},
year = {2000},
title = {My Article},
booktitle = {My Book},
}
\end{filecontents}
\usepackage[turkish, shorthands=:!]{babel}
\usepackage[backend=biber]{biblatex}
\addbibresource{biblio.bib}
\begin{document}
Hello! \cite{Doe}
\printbibliography
\end{document}
It seems that it would be enough to change {i\c{c}inde} into {\.{\i}\c{c}inde} within turkish.lbx (it's 4 times there).
Thanks for reporting this. I'm guessing it has to do with the case changing code switching between releases. It would be a bit painful to have to mark up each i as \.{i} in turkish.lbx. I'm wondering if we couldn't somehow use the language-specific commands here. (Plus I'm now wondering why it used to work before. Did babel-turkish enforce a different case changer?)
In particular
\documentclass[a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[turkish, shorthands=:!]{babel}
\begin{document}
\MakeUppercase{i\c{c}inde}
\MakeUppercase{\.{i}\c{c}\.{i}nde}
\end{document}
also seems to have changed between TeX Live 2021 and TeX Live 2022 (as available on Overleaf).