BIMcollab does support special characters, but it depends on the encoding of the file that you want to import.
Like most web applications, BIMcollab uses Unicode encoding to ensure that all special characters are supported and can be displayed correctly. However, since some software (like Microsoft Excel) does not always use 'Unicode' to export data to CSV format, BIMcollab sometimes encounters difficulties in recognizing certain special characters in these files that are not in Unicode.
To resolve this problem, you should consult the documentation of the software with which you exported the CSV file, and check if you can redo the export of your data using Unicode encoding.