UTF-8 is capable of encoding any codepoint in the Unicode range. UTF-16/32 cannot be used over IRC because they require the use of NUL bytes which IRC as a text-based medium does not support, meaning UTF-8 is the only viable Unicode encoding for IRC.
"UTF-8 BOM" isn't an encoding. BOM stands for Byte-Order Mark and is used for UTF-16 and UTF-32 to signify
endianness. UTF-8 does not require a BOM (although it is sometimes used simply to show that the text is UTF-8 encoded).
