I don't have any info that you can do it with SQL Server database settings, SQL Server doesn't change its behavior depending on regional settings in this case the decimal symbol!

But you can retrieve the data from database with REPLACE Function like here:

DECLARE @N VARCHAR(12)

SET @N = '123456,789100'

SET @N = REPLACE(@N, ',','.')

SELECT @N

===

Reverse option:

DECLARE @m VARCHAR(12)

SET @m = '123456.789100'

SET @m = REPLACE(@M, '.',',')

SELECT @m

OR

just use the Replace Function on the field where you have the number with decimals like

SELECT REPLACE(YOUR_FIELD, ',', '.')

You can change , or . and vice-versa!