Cursor and selections visualized with offset on lines with swedish characters

[Yakimych]

I've been trying to edit text in Swedish with oni2 and noticed that sometimes the cursor was being shown incorrectly when jumping by word or even searching with / or ?. The reason seems to be that every swedish character adds an extra offset to the cursor position. This is also a problem in visual mode and when highlighting searches:

This offset gets returned from native code, and unfortunately I don't understand much of C code, but I ended up in e.g. normal.c: https://github.com/onivim/libvim/blob/master/src/normal.c#L4534 (in case this helps).