How do I set default language NOT in the url (i.e. WITHOUT appending e.g. "?locale=he")

[MichaelLev]

I develop on EXB 1.13 Developer Edition.

I want that WITHOUT appending "?locale=he" to the end of the application's url,
the default language will be Hebrew (instead of English)

and that by appending "?locale=" then the language will be taken from the url

How can I code it?