Files contain bytes. If you want to write a text string to a file, the string needs to be converted from text to bytes. That's what the >:encoding(UTF-8) does.

OTOH if you want to read data from a file, without the :encoding(UTF-8) the string will contain bytes, and with it the string contains text.

Sad thing is, you can't reliably see from looking at a string if it's text or bytes. And if you mix the two up, you will see some broken output.

So if you use text strings internally in your program, you need the :encoding(UTF-8) both for reading and writing files, and you need to decode all other byte strings that come into your program (for example with %ENV or @ARGV).

OTOH some modules already decode strings for you (for example XML and JSON parsers), so you must be aware which module does that.

I found in some Russian article to add this line
use encoding 'UTF-8'
in each file ... Now all works
Thanks for all

I don't think anyone can tell you precisely when you need to add an encoding layer on files open for read because it depends on whether the data in the input file is UTF-8 (in your case) encoded or not. If private_data is UTF-8 encoded then you need to add the UTF-8 encoding layer to decode it on input. If path_index is intended to be UTF-8 encoded file you need to encode the data when writing it.

When you say "prints all the data into HTML page" are you running some sort of CGI, in web server code because if you are you need to set the the doctype in the HTML and probably on the content-type too.