This is an analyzer and codefixer for Russian letter C in English word and vice versa.

An appropriate nuget can be found here

Insert to your Directory.Build.props the following:

  <PropertyGroup>    
    <WarningsAsErrors>RussianC;EnglishC</WarningsAsErrors>
  </PropertyGroup>

...

  <!-- анализатор некорректного использования букв C/С -->
  <ItemGroup Condition="'$(MSBuildProjectExtension)'=='.csproj'">
    <PackageReference Include="FixRussianCAnalyzer" Version="0.2.0">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
    </PackageReference>
  </ItemGroup>

If you need to disable this analyzer in concrete file\lines you may add #pragma warning disable RussianC or #pragma warning disable EnglishC to the appropriate place.