Why does the encoding break?

Question

Notepad++

Good afternoon.
1) I open a file (notepad ++) encoding win-1251, write the text there, save it, close the file.
2) I open the file - Macintosh encoding. (And you need win-1251)
As far as I understand, there are characters in the text that lead to this behavior.
How to calculate them?
Text example:

{
    "in": ["param1"],
    "in_out": ["param2"],
    "out": ["param3"],
    "inDescr": "--   Установить $x$ в $y$;",
    "outDescr": "--   Значение $x$ установлено в $y$;",
    "outDescr2": "--   Значение $x$ не изменилось;",
    "outDescr3": "--   Значение $x$ установлено в $y$ с погрешностью $z$;",
    "inArr": "--   Установить $x$ следующим образом: $y$;",
    "outArr": "--   Значения $x$ установлены следующим образом: $y$;",
    "outArr2": "--   Значения $x$ не изменились;",
    "inStub": "--   Функция $x$ возвращает значение $y$;",
    "outStub": "--   Функция $x$ не вызывалась;",
    "outStub2": "--   Функция $x$ вызывалась $y$ раз с параметрами ($z$"
}

Answer 1

You are misinterpreting the situation.
Nothing happens to the file encoding, it's just that Notepad++ erroneously automatically recognizes it when it is reopened. Just change it. In your file, the encoding is not specified anywhere, so he guesses (incorrectly).