VSCode C++ Intellisense hover doxygen preview encoding issue

Question

I have C++ files saved with Windows1251 encoding. When I hover over a doxygen-documented function, in the preview window there are question marks only. I can't seem to find a setting for that. Any suggestions?

Reproduction

1. First of all, doc comments have to be in cyrillic.
2. Doc comments have to be in a separate file (let's call it header.h). Not the active one where I'm hovering.
3. There should not be an open tab with header.h in VSCode. If you have one, the hover-on preview seems to work.

Example

header.h:

/// @brief  Сумма 2 чисел
/// @param a Число 1
/// @param b Число 2
/// @return Сумма чисел 1 и 2
int sum_int(const int a, const int b)
{
    return a + b;
}

test.cpp:

#include "header.h"

void main()
{
    sum_int(1, 2);
}

Hovering over sum_int in test.cpp provides the following window:

int sum_int(int a, int b)
����� 2 �����

Parameters:
a – ����� 1
b – ����� 2

Returns:
����� ����� 1 � 2