No, there is no direct way to assign javascript variable to JSTL/JSP.
Java runs on the server, produces an HTML page.
Javascript runs on the client.
The only way to pass information from client to server is to make an HTTP request - which is the basis of ajax.
My suggestion for a workaround would be to do your i18n in Spring, providing the message "The time is currently [insertTimeHere]" or "It is [insertTimeHere] where you are right now"
That message can get output onto the html page in a javascript variable.
You then get the current time from the client, and use
string functions to replace [insertTimeHere] with the time from the client.
So you will be able to localize the message part of "The time is currently..." with Spring but not the actual time string (got from the client)
Does that suffice?