Currently, the RadSpreadsheet supports only Dollar as currency. 

As a temporary workaround, the Kendo UI Spreadsheet (https://demos.telerik.com/kendo-ui/spreadsheet/index) can be used as demonstrated in this Dojo example: https://dojo.telerik.com/imAWasuJ

- Select a cell with number as value 
- Open the formats dropdown 
- Choose the "More Formats..." option 
- Select "Currency" tab
- Choose a currency from the dropdown
- Choose the desired format.