It’s well-defined, at least in the terminal: the east-asian characters are simply double the normal width. There’s a Unicode property to decide which is which: https://www.unicode.org/reports/tr11-2/
They still line up (when rendered with correct double-width), the east-asian characters just take up two “slots”, as if they were two normal characters. I don’t know if you see a problem with that, or if you’re talking about renderers and/or applications that don’t correctly handle this double-width logic.
My point is that if handled correctly, e.g. in terminals, there is no problem with that, as long as the application is double-width aware. For example I use Mutt as a mail reader in a terminal, with Vim as an editor, and mixed latin and east-asian characters work fine with them and line up on the terminal grid.
I don't think I've ever seen a double-width font outside of an actual terminal emulator though. It's really frustrating that the fonts used by all IDE's and graphical emacs/gvim/vcode seems have this mixed script spacing issue.
