hyperref: Trouble when Using English in Chapters/Sections (Greek document)

Question

I'm writing my thesis in latex (greek document) and I have trouble with hyperref when I put English words in chapters and sections. This problem goes away if I use only greek characters .here is a minimal example with my actual preamble

\documentclass[a4paper,oneside,11pt]{book}
\usepackage{ucs}
\usepackage{amsmath,amssymb}
\usepackage{xfrac}
\DeclareMathOperator{\arcsinh}{arcsinh}
\usepackage{bm}
\usepackage[utf8x]{inputenc}
\usepackage[greek,english]{babel}
\newcommand{\en}{\selectlanguage{english}}
\newcommand{\gr}{\selectlanguage{greek}}
\usepackage{graphicx}
\usepackage{fancyhdr}
\usepackage{epigraph}
\pagestyle{fancy}
\fancyhead{}
\fancyhead[R]{\thepage}
\fancyfoot{}
\usepackage{pdfpages}
\usepackage{kerkis}
\usepackage[unicode]{hyperref}

\begin{document}
\gr

\chapter{τι κάνεις {\en {Hello}}

καλημέρα\cite{alice}

\begin{thebibliography}{9}
\bibitem{alice}  \en
Carol L.,Alice in,Wiley
\end{thebibliography}


\end{document}

Answer 1

\selectlanguage (used by \en and \gr) does not work in bookmarks. It can be disabled after loading hyperref:

\pdfstringdefDisableCommands{\let\selectlanguage\@gobble}

Also, since assignments do not work in bookmark strings, the needed code page needs to be loaded for ucs/utf8x. Either \PreloadUnicodePage or \PrerenderUnicode can be used:

\PreloadUnicodePage{3}

Third, the curly braces do not match in the first \chapter line. Either an additional closing brace is needed at the end of the line, but \en does not have an argument and group braces around Hello are not needed. Therefore, the simpler fix is to remove the opening curly brace before Hello.

Summary:

\usepackage[unicode]{hyperref}
\pdfstringdefDisableCommands{\let\selectlanguage\@gobble}
\PreloadUnicodePage{3}
...
\chapter{τι κάνεις {\en Hello}}