Clarify error messages for column name errors in csv import

[LaszloKecskes]

It has been reported that if a "label with the language code is misspelled", the following error happens: "Cannot read properties of undefined (reading 'type')". The import does not happen.

The task is to clarify the error message for this case.

[RafaPolit]

There is a concern that, even if the text would be better, it will only show for a few seconds in the screen and the user may miss it altogether. @konzz has suggested that we spend time in a "CSV Import Report" that would help us mitigate all these problems we keep on fixing with the import process.