Currently, when the "Custom format" button in the Spreadsheet is clicked, the available predefined formats that can be applied to a cell appear as demonstrated in the below screenshot. These predefined options don't change if you set a specific Kendo UI culture. 

It will be a very useful feature to be able to change the predefined custom formats. Also, it will be nice if the custom formats in the Spreadsheet can be set based on the selected Kendo UI culture.