Short version
locale was set using KDE but no such thing exists in /usr/share/locale.
Long version
I have setup my locale using the settings window like the following:
Checking the locale would show:
locale: Cannot set LC_ALL to default locale: No such file or directory LANG=en_US.UTF-8 LC_CTYPE="en_US.UTF-8" LC_NUMERIC=en_US.UTF-8 LC_TIME=en_FI.UTF-8 LC_COLLATE="en_US.UTF-8" LC_MONETARY=en_FI.UTF-8 LC_MESSAGES="en_US.UTF-8" LC_PAPER=en_US.UTF-8 LC_NAME=en_US.UTF-8 LC_ADDRESS=en_US.UTF-8 LC_TELEPHONE=en_US.UTF-8 LC_MEASUREMENT=en_FI.UTF-8 LC_IDENTIFICATION=en_US.UTF-8 LC_ALL=
I then realized some softwares stopped working and/or throwing errors including rofi and R.
I’m no expert, but according to many developers [1, 2] and community [3]:
en_FIis not a valid locale to begin with.
While searching I stumbled upon the following:
- ICU Locale “English (Finland)” (en_FI)
- Ubuntu Manpage: DateTime::Locale::en_FI - Locale data examples for the English Finland (en-FI) locale
I would like to emphasize that the en_FI.UTF-8 should be a thing (if it is not already) as not everyone living in Finland speaks Finnish. (fi_FI, sv_FI are already there and en_FI is what many would need/want)

