It seems to have supported UTF-8 for at least a decade. Although it went the full-on ECMA-35 route of making that an optional switchable character set.

There was an issue back in 2016 where, ironically, it was coming up in Latin-1 mode with everything else around it talking UTF-8, and there have been other similar impedance mis-matches over the years. But they seem to hinge on it actually having UTF-8 support.

* https://github.com/cosmos72/twin/issues/4

* https://github.com/cosmos72/twin/issues/7

* https://github.com/cosmos72/twin/issues/8

However: There was no 256 colours support as of 2021.

* https://github.com/cosmos72/twin/issues/30

And in some places it even required IBM code page 437.

* https://github.com/cosmos72/twin/issues/22

And some of the doco seems to have never been incorporated.

* https://github.com/cosmos72/twin/issues/100