My default system language is American English.
However I often use British English as well. And I often use Turkish in documents, browse Turkish websites, etc. But when I add these 2 languages Konsole starts displaying output partially in Turkish and - probably due to lack of translation - partially in English.
STEPS TO REPRODUCE
1. Go to "System Settings > Regional Settings > Language".
2. Add "British English", and then Turkish, i.e. "Türkçe".
3. Log out and back in.
4. Start Konsole, and enter "sudo apt update".
Konsole starts displaying output partially in Turkish and partially in English.
Konsole should use the language setting in "System Settings > Regional Settings > Formats > Region" or the first language in "System Settings > Regional Settings > Language".
Linux/KDE Plasma: Kubuntu 19.10
(available in About System)
KDE Plasma Version: 5.18.3
KDE Frameworks Version: 5.67.0
Qt Version: 5.12.4
I might have seen this problem elsewhere in among KDE apps but I don't remember now...
*** This bug has been marked as a duplicate of bug 327757 ***
*** This bug has been marked as a duplicate of bug 192019 ***