It is a Ruby implementation of RFC 2047, which is more accurate and fault-tolerant than ConradIrwin/rfc2047-ruby. The former can encode, decode, and handle charset correctly, while the latter only implement decoding function.
gem install new_rfc_2047
Rfc2047.encode('己所不欲，勿施於人。')
# => "=?UTF-8?B?5bex5omA5LiN5qyy77yM5Yu/5pa95pa85Lq644CC?="
Rfc2047.decode '=?UTF-8?B?5bex5omA5LiN5qyy77yM5Yu/5pa95pa85Lq644CC?='
# => "己所不欲，勿施於人。"