Select2 has translation files.
As example this one:
http://demo.plone.org/++plone++static/components/select2/select2_locale_de.js
How to make the select2 translation active in plone 5.2?
I can see also not used in the demo.plone.org:
http://demo.plone.org/de/frontpage/edit?_authenticator=829e6a35eee89498daa8c2808468fb3c3c809659&set_language=de#autotoc-item-autotoc-4
("ersteller" field).