[Plasma locales choices] have replaced the former method of customizing date - time formats. Typical user needs are for 24 hr time notation, and ISO date format. This means that the %HH and other choices are no longer accessible across KDE Plasma. The Plasma format choices among the locales also correspond to certain language choices. Thus, it may be possible to find a usable date - time format, but that often forces an unwanted language selection.
This is a well-known user gripe. Several releases of Plasma have occurred since this was identified, and no customizing options are in sight. Some folks have stated the snag is due to the QT implementation in Plasma. Various user groups have shared their unhappiness on this issue.
Please comment on how we might again have full customizing of the date and time formats. Better, tell us how you have worked around this dilemma. My implementation is Fedora 25, fully-updated daily. Thanks.