Where to translate SHOW DETAILS from a display view?
This string seems to be a part of the interface, so you can translate it through Configuration » Regional and language » Translate interface (/admin/config/regional/translate/translate).
You have to enter the exact capitalisation into the search as is written in code (it's case sensitive), not necessarily what you see on the screen (CSS can affect what capitalisation is used in display).
The string won't appear on this list unless you have visited a page with that string in another language (other than English) so Drupal picks it up and makes it available for translation.