Confirmed, we currently decide paper size with measurement system, QLocale::ImperialUSSystem and QLocale::ImperialSystem are treated as "Letter", the rest "A4". Qt doesn't provide a direct method to determine paper size from locale.

Hm, so should this be a bug in Qt then?

I don't think so, but if Qt exposes Paper size via QLocale API, this bug can be fixed with ease.

So it's not so much that this is a bug in Qt, but an omission in Qt causes us to do something ourselves and therefore introduce the bug.

Since the code is under our control, we could add an exception to this code that says "Use Letter if the locate is Canada". It would be ugly, but feasible. And then we can remove it once Qt grows the functionality we need.

I ran a script across locales available on Arch Linux, it seems the locales below all suffers from the same problem:
en_CA
en_PH
es_BO
es_CL
es_CO
es_CR
es_GT
es_MX
es_NI
es_PA
es_PR
es_SV
es_VE
fil_PH
fr_CA
ik_CA
iu_CA
miq_NI
nhn_MX
shs_CA
tl_PH

A possibly relevant merge request was started @ https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/4458

Git commit c7421fcd8823c595f047fab64c14d075db008b2b by Han Young.
Committed on 18/06/2024 at 05:10.
Pushed by hanyoung into branch 'master'.

kcm_regionandlang: fix incorrect paper size example for some locales

kcm_regionandlang: fix incorrect paper size example for some locales

We decide paper size with measurement system, QLocale::ImperialUSSystem and QLocale::ImperialSystem are treated as "Letter", the rest "A4". Qt doesn't provide a direct method to determine paper size from locale. However, some locales use metric measurement system but Letter for paper size. Put these locales in a QSet and return 'Letter' for paper size example.

M  +28   -1    kcms/region_language/exampleutility.cpp

https://invent.kde.org/plasma/plasma-workspace/-/commit/c7421fcd8823c595f047fab64c14d075db008b2b

Git commit fb7f8557cc14a190f0ef5f8dd0c166b224446cc3 by Han Young.
Committed on 18/06/2024 at 05:33.
Pushed by hanyoung into branch 'Plasma/6.1'.

kcm_regionandlang: fix incorrect paper size example for some locales

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### Original commit message(s)

* kcm_regionandlang: fix incorrect paper size example for some locales

kcm_regionandlang: fix incorrect paper size example for some locales

We decide paper size with measurement system, QLocale::ImperialUSSystem and QLocale::ImperialSystem are treated as "Letter", the rest "A4". Qt doesn't provide a direct method to determine paper size from locale. However, some locales use metric measurement system but Letter for paper size. Put these locales in a QSet and return 'Letter' for paper size example.


(cherry picked from commit c7421fcd8823c595f047fab64c14d075db008b2b)

eaf58e75 kcm_regionandlang: fix incorrect paper size example for some locales
75ff8016 Apply 1 suggestion(s) to 1 file(s)
979cd1d8 improve readability

Co-authored-by: Han Young <hanyoung@protonmail.com>

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M  +28   -1    kcms/region_language/exampleutility.cpp

https://invent.kde.org/plasma/plasma-workspace/-/commit/fb7f8557cc14a190f0ef5f8dd0c166b224446cc3