Encoding scheme used for cookies

Question

RFC 6265 Sec 6.1 specifies allowing atleast 4096 bytes per cookie.

Now in order to know the number of characters allowed per cookie, I need to know

Answer 1

It seems it is determined more by the programmer (behind the browser) than by the programming language. Usually cookies values are URL-encoded but there is no requirement.
Have a look at this answer that complete your study (adding the Safari special case). This one might help too.