Hi @k-okada,
No, you are not missing anything. You can already pass non-ASCII strings through the string type on ROS2 (and ROS1, for that matter).
The downsides of the current approach, however, are that the publishers and subscribers don’t know the encoding of the data they are sending/receiving. If you have a system where everything is UTF-8, then things are just fine, but if you might have strings with different encodings, it can be hard to determine which encoding is coming from which source.
Additionally, C++ has pretty poor support for dealing with Unicode strings. It would be nice to have ROS2 have better API support for dealing with Unicode.
All of the above is laid out in this PR: https://github.com/ros2/design/pull/117 . I am looking for feedback on what parts of this are useful, what kinds of problems people have had with Unicode and ROS1 in the past, etc. Any feedback you (and others) could provide would be great.