Store A Long String Of Text Into A Local Storage Member On A Browser - Character Data Sizes In JS

Lets say I wanted store a long string of text into a local storage member on a browser using javascript.

window.localStorage.setItem("key",longStringText);

Now lets assume that the text itself contains characters outside of the normal ISO-8859-1 character set (like asian or russian characters). Would the individual char values be stored as one byte or two bytes?

"hello" -> 5 * 1 bytes = 5 (normal 8859 character sets)
"hello" -> 5 * 2 bytes = 10 (unicode or an extended character set size).

Is ISO-8859-1 still stored like ASCII once was as 8 bits? Or is it 16? If I was to use a 2 byte character set then would that cut the size of my allocated local storage space by half?