Hiho,
Since I couldn't really find it on otland and people request like 1000 euro for that simple thing, here we go:
Open protcolgame.cpp
go to
change this:
to
go to
change this:
to
and
change this
to
go to
change this
to
go to
change this
to
and
change this
to
go to
change this
to
and enable the feature in features.lua
I hope I didn't forget anything 
Since I couldn't really find it on otland and people request like 1000 euro for that simple thing, here we go:
Open protcolgame.cpp
go to
C++:
void ProtocolGame::sendChannelMessage(const std::string& author, const std::string& text, SpeakClasses type, uint16_t channel)
C++:
msg.add<uint16_t>(0x00);
C++:
msg.add<uint32_t>(0x00);
go to
C++:
void ProtocolGame::sendCreatureSay(const Creature* creature, SpeakClasses type, const std::string& text, const Position* pos/* = nullptr*/)
C++:
msg.add<uint16_t>(speaker->getLevel());
C++:
msg.add<uint32_t>(speaker->getLevel());
change this
C++:
msg.add<uint16_t>(0x00);
C++:
msg.add<uint32_t>(0x00);
go to
C++:
void ProtocolGame::sendPrivateMessage(const Player* speaker, SpeakClasses type, const std::string& text)
C++:
msg.add<uint16_t>(speaker->getLevel());
C++:
msg.add<uint32_t>(speaker->getLevel());
go to
C++:
void ProtocolGame::sendToChannel(const Creature* creature, SpeakClasses type, const std::string& text, uint16_t channelId)
C++:
msg.add<uint16_t>(speaker->getLevel());
C++:
msg.add<uint32_t>(speaker->getLevel());
change this
C++:
msg.add<uint16_t>(0x00);
C++:
msg.add<uint32_t>(0x00);
go to
C++:
void ProtocolGame::AddPlayerStats(NetworkMessage& msg)
C++:
msg.add<uint16_t>(player->getLevel());
C++:
msg.add<uint32_t>(player->getLevel());
and enable the feature in features.lua
LUA:
g_game.enableFeature(GameDoubleLevel)
