You can do a feature request on github if you like, it might help me not to forget about it.
The primary site for ROXTerm is now realh/roxterm on github. I suppose I should change the SF site to redirect people, but I just never got around to it. Anyway, the change in behaviour is caused by VTE. https://gitlab.gnome.org/search?search=vte_terminal_select_all&nav_source=navbar&project_id=1893&group_id=8&scope=issues. It's supposed to be a temporary hack to prevent a crash in gnome-terminal, but they've failed to fix the issue in a reasonable time. There is a function to write the entire buffer...
There are tags for the versioned releases. Usual practice is to clone the whole repository then check out the revision you want: git clone https://github.com/realh/roxterm.git cd roxterm git fetch --tags git checkout 3.6.2 But have you tried luit and found it definitely doesn't suit your needs? That seems to be standard practice for using legacy encodings in a UTF terminal, and you should get better reliability and features by using that with an up-to-date terminal.
There are newer versions of roxterm at its new home on github. I like to think the UX generally improves over time, and there are definitely some good reasons to use a version post 3.5.0, when I found a way to fix the shrinking window bug. That was caused by a change in GTK and also affected other terminals. I also replaced the build system with CMake, so that should cause you less bother with incompatibilities in BSD etc. The bad news is that I didn't bother supporting the translation infrastructure...
Supporting multiple encodings was deprecated in vte and has probably been removed by now. So having a version of roxterm that can still be compiled on a modern OS is a good idea. You can use luit to get your legacy programs to work in a UTF-8 terminal. I think having such a tool concentrating on this task is an improvement over relying on every terminal supporting as many encodings as possible.
Sorry I didn't realise it was a joke. You should have known that most programmers are autistic! Usually my sense of humour is quite good, but I tend more to dark humour (can get quite sick actually). Interesting about the pronunciation of 'ei'. I started thinking about names ending in -stein. Both syllables of Einstein always rhyme with "pine", even in America, don't they? What about Brian Epstein (the Beatles' manager). I've only ever heard that pronounced the Germanic way. But I know -stein names...
"Colour" is the correct spelling in the UK. I live with other programs and libraries using "color", but I didn't want to use foreign spelling in my own code. You could create an en_US translation for it, but all the other translators faded away, so I stopped payng much attention to the translation infrastructure, which never played well with SCM. The config path names shouldn't be translated though, these are effectively hidden files. Translating them would make things harder if you wanted to use...
Roxterm parses the geometry itself, so it should always interpret it as characters. It's possible you're using a very old version which used a, now deprecated, parsing function built into GTK. This sourceforge project is no longer active, you should use https://github.com/realh/roxterm instead. Hopefully you'll get a more consistent experience with a newer version, unless you're stuck with a very old version of GTK/GNOME on Solaris or something.