First two patches can be applied. The second patch is not mine, I just cherry-picked it from wchar branch.
Third patch changes internal representation in Glyph and makes it work. Fourth patch changes some functions mostly in the way already done in wchar branch. The general idea is to decode UTF-8 when reading from tty or clipboard and encode to UTF-8 when writing to terminal or clipboard. One problem is CSI and STR sequences. Now they are stored encoded to UTF-8 and i am not sure it should be changed because it makes it possible to use atoi to parse arguments. So tputc still encodes the character that was decoded a bit earlier. However, the code becomes simplier this way, lots of ugly '.c[0]' are replaced by '.u' and utf8len is removed. I think these patches can already be applied.
