Describe the feature you'd like to add to nginx

sub_filter should leave the page content untouched when processing e.g. pages with multi-byte characters like utf-8

Describe the problem this feature solves

Currently after rewriting URLs with sub_filter, special (multi-byte) characters get destroyed and show as "?" in the browser. In my case some pages even get completely unusable as they use utf-8 in more vital sections of the page