Some people here seem to think that indexing, measuring and slicing operations based on runes (code points) instead of bytes (UTF-8 code units) by default would be to be a good idea. It's not - you get the worst of both worlds: indexing is not a constant-time operation and a code point is still not a user-perceived character, because combining character sequences consist of multiple code points, even normalization doesn't help in general.
Other languages like C# seem to be different on the surface, but in fact they index and measure by code units as well (2 byte UTF-16 code units), not by code points.
Other languages like C# seem to be different on the surface, but in fact they index and measure by code units as well (2 byte UTF-16 code units), not by code points.