glossary duplicate term when translated in italic

Highly related to: https://github.com/sphinx-doc/sphinx/issues/7418

To Reproduce

$ wget -O- https://mdk.fr/x/2to3.tar.bz2 | tar -xjvf -
$ cd 2to3
$ sphinx-build -b html -qW -D locale_dirs=locales -E -D language=fr  . build/html
Warning, treated as error:
2to3/glossary.rst:8:duplicate term description of 2to3, other instance in glossary

This is due to 2to3 being translated *2to3*.

Expected behavior

I don't expect translation to interfer term linking.

Your project

We found this one on https://github.com/python/python-docs-fr, but it's easier to reproduce using our minimal reproducer.

Environment info

• OS: Debian
• Python version: 3.9

We tried multiple Sphinx releases (upstream, not with my reproducer):

• Sphinx==2.4.4: it works
• Sphinx==3.2.1: duplicate term when translated error
• Sphinx==3.3.0: It works
• Sphinx==3.3.1: It works
• Sphinx==3.4.0: duplicate term when translated error
• Sphinx==3.4.1: duplicate term when translated error
• Sphinx==3.4.2: duplicate term when translated error
• Sphinx==3.5.1: duplicate term when translated error

Start with the minimal reproducer's glossary.rst and run the documented sphinx-build command using the affected Sphinx versions. Trace how the translated italic term is registered and compare it with the working versions; done means the French build completes without a duplicate term description warning.