Language setting isn't respected on URL field of biblatex reference

Question

I am currently writing my thesis in Greek, but I have to cite mostly English sources. My bibliography file looks like this:

@online{microsoft-memory-safety-errors,
    author={\en{MSRC Team}},
    title={\en{A proactive approach to more secure code}},
    url={\en{https://msrc-blog.microsoft.com/2019/07/16/a-proactive-approach-to-more-secure-code/}},
    year={2019},
    month={7}
}

Although \en{} works fine for the author and title fields, it fails to work with the URL field, creating the reference as follows:

MSRC Team. «A proactive approach to more secure code». (Ιούλ. 2019), διεύθν.:
%5ἓν%7Βηττπς://μσρς-βλογ.μιςροσοφτ.ςομ/2019/07/16/α-προαςτιvε-αππροαςη-
το-μορε-σεςυρε-ςοδε/%7Δ.

main.tex:

\documentclass[11pt,a4paper,english,greek,twoside]{book}

\usepackage[greek]{babel}
\usepackage[utf8]{inputenc}
\usepackage[backend=biber,style=ieee]{biblatex}
\addbibresource{chapters/bibliography.bib}

% typeset short english phrases
\newcommand{\en}[1]{\foreignlanguage{english}{#1}}

\selectlanguage{greek}

\begin{document}
    Κείμενο \en{Text}\cite{microsoft-memory-safety-errors}
    
    \printbibliography
\end{document}

Answer 1

For entries which are fully english, consider to use the langid field and the language option of biblatex to switch the language. This will also translate for example the date. The effect can be seen in the first entry.

If you prefer to switch to english only for special fields with your \en command: don't use it for an url, that will simply break.

url's should typically always be in a latin/ascii so the easiest is to switch the encoding in \UrlFont.

I used article as class to get everything on one page.

\documentclass[11pt,a4paper,english,greek,twoside]{article}
\usepackage[greek]{babel}

\usepackage[style=ieee,language=auto,autolang=other]{biblatex}
\addbibresource{test.bib}

% typeset short english phrases
\newcommand{\en}[1]{\foreignlanguage{english}{#1}}

\usepackage{xurl} %more break points 
\renewcommand\UrlFont{\fontencoding{T1}\ttfamily}


\begin{document}

    \url{https://msrc-blog.microsoft.com/2019/07/16/a-proactive-approach-to-more-secure-code/}
    
    Κείμενο \en{Text}
    
    \cite{microsoft-memory-safety-errors}
    \cite{microsoft-memory-safety-errors-var}

    \printbibliography
\end{document}

used bib entries

@online{microsoft-memory-safety-errors,
    author={MSRC Team},
    title={A proactive approach to more secure code},
    url={https://msrc-blog.microsoft.com/2019/07/16/a-proactive-approach-to-more-secure-code/},
    year={2019},
    month={7},
    langid={english}
}

@online{microsoft-memory-safety-errors-var,
    author={\en{MSRC Team}},
    title={\en{A proactive approach to more secure code}},
    url={https://msrc-blog.microsoft.com/2019/07/16/a-proactive-approach-to-more-secure-code/},
    year={2019},
    month={7},
}