Decimal separator, dot to comma

Just a guess here but are those numbers actually numbers or are they text that look like numbers? I am thinking the decimal did not change to a comma as expected because Numbers considers those cells to be text/strings, not numbers. Being from a CSV file, that would not be unheard of. Try selecting those cells and changing the format to a number format.

An easy test if you are not sure if they are numbers or not is to insert a new column temporarily and in that column use the SUM function on each number (for example =SUM(B2) ). The sum will be zero if the cell has text, it will equal the number if the cell has a number.

Here is what I tried:

My system settings use the decimal point. If I import a CSV that has numbers that use a comma for the decimal (the CSV therefore uses a semicolon, not a comma, to separate the columns), it imports as a total mess until I adjust the import settings and choose the semicolon as the separator. After adjusting the settings, the "numbers" get imported to the correct cells but as text and the cell format cannot be changed to "number". If I change the region for the document (File/Advanced/Language & Region), choosing a region that uses the comma, I can then change the format of those cells to "number" and the format sticks, they become numbers.

Doing this a different way, if I start out with a new document, change the region, then drag a CSV onto a sheet or table (adjusting the import settings as before), the numbers start out as numbers without me having to change the cell format.

I mention the second method because it might make the job easier in the future if you create a template for these CSV imports. I did not try it but I assume you could set up a document with an empty table and with the region set correctly and save it as a template. You could use that template to import your CSV files. You would create a new document from the template then drag the CSV to to empty table to import it.