Not sure what you compare CHAT_ROUTER to here?
CHAT_SYSTEM?
It's only left over as compatibility alias to the newer KEYBOARD_CHAT_SYSTEM, which is an object of the newer class ZO_ChatSystem.
https://github.com/esoui/esoui/blob/...iases.lua#L820
And CHAT_ROUTER is ZO_ChatRouter which handles formatting etc. now.
https://github.com/esoui/esoui/blob/...dlers.lua#L167
Not sure what causes the client crashes here, maybe code page differences. I also remember there was a chat related issue Sharlikran worked on in the gitter.im/esoui/esoui channel with some Korean/Chinese dev. They found out there needs to be fixed something and I think this was done on PTS already.
Are you able to reproduce the crash on live and PTS? Maybe it's the same that Sharlikran noticed and it's meanwhile fixed on PTS?