I was struggling with a problem when programming PowerApps testapp.
When using formulas, I did as examples suggested, but ran into errors all the time.
I then tested to change the comma separator in formula to semi-colon and the formula worked.
PLEASE: Do not do the same stupid mistake with PowerApps coding as there is in Excel. Keep the separators the same, do not try to find "localized" names for functions etc. THIS IS STUPID and a waste of time, both for developers in Microsoft and also here, where we have to try to adapt to such. The programming is slower, the examples or things found in Internet do not work similarly etc.
It has been a stupid decision for Excel, do not do the same thing for PowerApps. (I used the DateValue() function and it did not work before I changed the comma (,) in the formula to semi-colon (;) which is not told in any documentation. (as it is not in Excel documentation either).
My localization language is something else than English. Do not know what. (seems it cannot be changed)
BTW use internationally standardized formats as default when presenting for instance dates and time.
(there were two suggestions, can live with the latter, the first is a PITA)