is_utf8?

# File activesupport/lib/active_support/core_ext/string/multibyte.rb, line 38
  def is_utf8?
    case encoding
    when Encoding::UTF_8
      valid_encoding?
    when Encoding::ASCII_8BIT, Encoding::US_ASCII
      dup.force_encoding(Encoding::UTF_8).valid_encoding?
    else
      false
    end
  end