CUPS web interface using wrong language / locale (Kubuntu 19.04)

Problem: the CUPS web interface (http://localhost:631) is in pt-BR, when I want the language for my system interface set to en-US.

I live in BR, so I set regional fields (time template, currency, name order, address, telephone, units of measure, paper options etc.) to pt-BR, but not the system language:

$   localectl System Locale: LANG=en_US.UTF-8                LANGUAGE=en_US                LC_NUMERIC=pt_BR.UTF-8                LC_TIME=pt_BR.UTF-8                LC_COLLATE=pt_BR.UTF-8                LC_MONETARY=pt_BR.UTF-8                LC_PAPER=pt_BR.UTF-8                LC_NAME=pt_BR.UTF-8                LC_ADDRESS=pt_BR.UTF-8                LC_TELEPHONE=pt_BR.UTF-8                LC_MEASUREMENT=pt_BR.UTF-8                LC_IDENTIFICATION=pt_BR.UTF-8    VC Keymap: n/a   X11 Layout: us    X11 Model: pc105  X11 Variant: alt-intl  $   cat /etc/default/locale LANG=en_US.UTF-8 LANGUAGE=en_US LC_CTYPE=en_US.UTF-8 LC_NUMERIC=pt_BR.UTF-8 LC_TIME=pt_BR.UTF-8 LC_COLLATE=pt_BR.UTF-8 LC_MONETARY=pt_BR.UTF-8 LC_MESSAGES=en_US.UTF-8 LC_PAPER=pt_BR.UTF-8 LC_NAME=pt_BR.UTF-8 LC_ADDRESS=pt_BR.UTF-8 LC_TELEPHONE=pt_BR.UTF-8 LC_MEASUREMENT=pt_BR.UTF-8 LC_IDENTIFICATION=pt_BR.UTF-8 LC_ALL=en_US.UTF-8 

In System Settings, in KDE, the Regional Settings panel is set to the following:

Language: only “American English (default)” appears.

Formats: Region is set to “United States – American English (en_US)”, and Number, Time, Currency, Measurement Units and Collation and Sorting is set to “Brasil – português (pt_BR)”.

I already used sudo dpkg-reconfigure locales, but the CUPS web interface is still using pt-BR language.

So, why is that? Where is the pt-BR setting coming from? It seems funny (to me) that this is only happening afaik in the CUPS web interface. Everything else in my system is in en_US as expected.

I rarely use the CUPS web interface, but this is bugging me. Thank you.