Thank you for the clarifications.
Regarding the number's format in the formula, unfortunately we support only numbers with dot "." as a decimal separator, no commas, regardless of the culture.
As for the excel import, what happens there is that the cells have no format at all. If you format them in Excel "#,##.00" and save the file, it should be fine on import. When there's no format defined, currently the Spreadsheet doesn't take culture into account - the browser itself just stringifies the number to 3.14.
If you consider that this should be built-in functionality of the Spreadsheet, I would suggest you to create feature requests in the Kendo UI UserVoice portal
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