SUMMARY
If system is set to a locale that uses comma instead of dot as decimal separator, functions like min() or max() which take multiple parameters won't work, as system thinks that comma is decimal separator rather than parameter separator.

STEPS TO REPRODUCE
1. Set decimal separator to comma in system settings -> regional settings -> formats -> numbers (i.e. pl_PL uses comma)
2. Try to plot anything using min or max, i.e. f(x) = max(sin(x),cos(x))

OBSERVED RESULT
Plot isn't drawn as kmplot complains about input being invalid

EXPECTED RESULT
Plot is drawn


SOFTWARE VERSIONS
(available in About System)
KDE Plasma Version: 5.14.1
KDE Frameworks Version: 5.51.0
Qt Version: 5.11.2

ADDITIONAL INFORMATION
Tested under pl_PL locale, when running LANG=C kmplot everything works as expected