I am using sources in multiple languages in my BibLaTeX bibliography (in this case French and English). The main language of my document is English.
In this situation, the references in French are spilling out of margins, even though I specified the langid parameter in my bib-file. Hereunder is a screenshot of the behaviour.

It appears that if I set French as the main language of the document, the problem is partly solved: the title displays correctly but the link is still spilling out of margins. This is the reason I think it is linked to the languages of my bibliography entries.
Do you know how to make my bibliography entries stay within margins, keeping English as the main language of my document?
Here are is a MWE:
\documentclass[11pt, a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[frenchb, main=english]{babel}
\usepackage[autostyle=true]{csquotes}
\usepackage[style=numeric, backend=biber, maxbibnames=10, sorting=nyt, autolang=hyphen]{biblatex}
\usepackage[top=2.2cm, bottom=2.5cm, left=2cm, right=2cm]{geometry}
\addbibresource{db.bib}
\DeclareFieldFormat{url}{\newline\url{#1}}
\DeclareFieldFormat{urldate}{\addcomma\space\bibstring{urlseen}\space#1}
\DefineBibliographyStrings{english}{
urlseen = {consulted on},
}
\begin{document}
Let's cite them all: \cite{ITU_climate} and \cite{ITU_2005}.
\printbibliography
\end{document}
And my bib-file:
@online{ITU_climate,
langid = {french},
author = {{International Telecommunication Union}},
title = {Rôle des télécommunications/technologies de l'information et de la communication en ce qui concerne les changements climatiques et la protection de l'environnement},
year = {2010},
url = {https://itunews.itu.int/fr/1794-Role-des-telecommunicationstechnologies-de-linformation-et-de-la-communication-en-ce-qui-concerne-les-changements-climatiques-et-la-protection-de-lenv.note.aspx},
urldate = {2015-21-11}
}
@online{ITU_2005,
langid = {english},
langidopts = {variant=british},
author = {{International Telecommunication Union}},
title = {Twenty Years of Measuring the Missing Link},
year = {2005},
month = {Oct.},
url = {http://www.itu.int/osg/spu/sfo/missinglink/kelly-20-years.pdf},
urldate = {2015-21-11}
}

\usepackage[hyphens]{url}doesn't really do anything in this case. Indeedbiblatex's URL setup allows breaks after hyphens (-is aBigBreakby default withbiblatex; it is aBigBreakwith theurlpackage if the package is loaded with thehyphensoption).microtypeis a great idea as always, though. – moewe Nov 23 '15 at 21:49