I have a fresh installation of Drupal 8.2.5 and want to use it for mostly Spanish content, but keeping the admin interface in English. /admin/config/regional/language says,
It is not recommended to change the default language on a working site.
And /admin/config/regional/language/detection/selected says,
Changing the site's default language itself might have other undesired side effects.
What will break if I change the default language? Or is a better question to ask, should I want to change the default language? I found this question, but it does not answer my question, aside from also being pre-Drupal8.