Ki18n kf5 branch fails to build

I am starting to play around with modifying kde software and for that purpose just set up kdesrc-build. When I tried to compile minuet or dolphin with it, building ki18n failed because it uses the kf5 branch, in which src/localedata/kcountry.cpp includes a header file that does not exist:

#include <private/qlocale_p.h>

Am I supposed to create this myself? And if yes, how?
Or is this a bug that I should report?

Or can I somehow force it to build with Qt/Frameworks 6 instead of 5?
Because that (main) ki18n version does not have this import and 5 will soon be obsolete anyways, so working with 6 makes more sense I guess?

Alright, I figured out how to make it build against qt6 (looking at the blog from Nicholas Fella). So I now don’t have that issue anymore, but I will leave this open in case it is a bug with i18n that I should report.

What does it involve to make this build successful? I am trying to install plasma 6 on kali as I am using wayland and want it to be fixed.
Any link or reference will be appreciated.