I just noticed something in Numbers 13.2, I wonder if it was there before.
If you open a CSV file which creates its own table, or create a table by pasting data from another source like Google Sheet, Numbers remembers what the data was like originally. So just after importing it shows that for a few seconds in the top-right corner of the sheet:
If the message has disappeared you can still find that at the bottom of the Format / Table side bar:
Clicking on either you're presented with this dialog window:
So if the source data has a decimal point but your language settings requires a comma instead just enter a point in the Decimal Separator field and the conversion is done immediately in the preview, and permanently in the table with Update Table. Quite handy. The other options can also make the importation a better success.