Thanks @wroos for your reply.
Many of the earlier discussions were related with proper UTF-8 incolding when exporting csv from Excel. I haven't found a discussion directly related to straight apostrophs.
But the problem persits even if the csv is exported from Visual Code as pure UTF-8. The "mistake" only occurs with straight appostophs ('), all other special characters liike é, è, ä, ö, ô work perfectly well.
My guess is, that Enketo interpretes the straight apostroph some sort as code and then fails on execution.
I saw that a new Web Form is in development that will replace Enketo. That's good news. Do we know for when the release is planned?