No it isn't:
> 10:48:55.380 document.location.href
> 10:48:55.384 "https://news.ycombinator.com/item?id=26166797"
> 10:48:57.723 document.characterSet
> 10:48:57.726 "UTF-8"
Plenty of non-ASCII symbols show up perfectly fine. For example, '£'.