Why is the text no longer readable after my modifications?

Question

C++ / C#

I get the element code from the site into a string variable and write it to a notepad, it turns out UTF_8, and the notepad itself chose the correct encoding, then I manipulate this string, or rather, remove all English characters and write it again to another notepad, let's call it notepad_2. This notepad_2 itself changes the encoding to ASCII, and all characters turn into rubbish, and the reverse conversion through "Save as" does not help, I don't know what to do.

Screenshot with text before modification

Screenshot with text after modification