Why pre/postfixes don't work and are shown as text on the webpage using Gulp4?

I'm trying to use libraries 'gulp-file-include' to include partials (header, footer) in my main html file. I'm also trying to use i18n using 'gulp-html-i18n'. Both partials and i18n seem working ("file-include" throws error when I'm trying to put the wrong path of file, or i18n creates lang directories). However when I try to wrap them into needed pre/postfixes, they are shown as plain text on the webpage.

Here is my gulpfile.js : Codeshare

Html:

<div>@@include('header.html')</div>

<div>$$</div>
</body>

Result:

from Why pre/postfixes don't work and are shown as text on the webpage using Gulp4?