As per the .NET format support shown here:
http://stackoverflow.com/questions/11731996/string-format-numbers-thousands-123k-millions-123m-billions-123b

And here:
http://msdn.microsoft.com/en-us/library/0c899ak8%28v=vs.100%29.aspx#SpecifierTh

123456789.ToString("#,##0,") will return "123,457".
123456789.ToString("#,##0,K") will return "123,457K".

kendo.format("{0:#,##0,", 123456789) will return "123,456,789".
kendo.format("{0:#,##0,K", 123456789) will return "123,456,789K".

As per the .NET standard, each trailing comma will round off 3 digits, so 123456789.ToString("#,##0,,M") will return "123M".

We'd like to be able to pass "Q" into the toString function for a date and have it return the quarter.

ex. 
kendo.toString(new Date(2000, 10, 6), "Q") -> Q4

As suggested here : http://www.telerik.com/forums/supporting-both-comma-and-dot-for-decimal-input
With this example : http://trykendoui.telerik.com/ikId/2

Having to force either the dot or comma for numerical input is cumbersome in applications where customers input data all day long and it has to be effective. 

I would suggest a flag named along the lines of "IgnoreCultureOnInput" which would allow you to punch in either the dot or the comma, but have it converted it back into your local for display. 

Note that the example above is not complete as it is : 
1 - locale specific (won't adjust if you locale calls for a comma instead)
2 - does not support text selection

Using a single minified culture file that would have all cultures supported by Kendo UI included can be very useful. Although it is possible do this manually by combining all files currently provided on official releases, this would have to be done every time Kendo UI is updated to a newer version. An official file would make things much more straightforward.

While dates and numbers can be formatted according to the current culture, kendo.getFileSizeMessage() has constant English strings '0 Byte' and 'Bytes'.

I suggest doing as Windows Explorer does: 0 as "0 KB", and any size between that and 1 KB as "1 KB".