Cyrillic letters in js and css

I’m trying to change "New item" form and show fields in two columns instead of one.
I find the solution here:
and try to implement it.
The major issue I have – column names shoud be in cyrillic letters. So I try to find the certain fields and replace it using js file and new html file like in the example but have "????" symbols in the output (see the pic attached).
How can I solve this? Thanks in advance.

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