Version
calcurse 4.8.1

Bug description.
The displayed text for when you save is not grammatically correct. It says:
"Data were saved successfully"
This is not correct as were is plural, the correct verb would be was, as it is singular. In this context data is singular so was should be used.

This also applies to other save messages

Reproduce.
Save a file.

Expected Behavior.
It should say "Data was saved successfully" when saved.

Screen Shot

I would make a pull request myself, but I was not able to get the program to compile. Probably a skill issue and something to do with me being on arm (asahi linux fedora).