How can I use a function like "Encoding - Convert to ANSI" in my code?

[gyrodrill]

I want to convert a UTF8 string to current system encoding, and “Encoding - Convert to ANSI” works perfect.
I’m trying to find how this function is implemented, but couldn’t find the file.
Is it in a part of github:src/WinControls/AnsiCharPanel? Or, reading which part of code may helps?