Character Translation Questions

[John Goerzen]

Hi folks,

I have a number of questions about the character translation feature
https://www.gnu.org/software/screen/manual/html_node/Character-Translation.html#Character-Translation
and the charset command
https://www.gnu.org/software/screen/manual/html_node/Character-Processing.html#Character-Processing

Context: I have a DEC vt420 that doesn't understand UTF-8.  I use screen
to provide a UTF-8 environment for applications and convert to
ISO-8859-1 for the vt420.  Unfortunately, ISO-8859-1 doesn't have some
common characters that people use in UTF-8 (em-dash, smart quotes,
etc).  It would be sensible to replace them with similar characters from
ISO-8859-1 instead of the question mark.

As I look at the character translation documentation, quite a few
questions arise:

1) What the heck is a "designator"?  It says B is ASCII, A is UK, K is
German, "etc".  I have never seen these kind of designators, and have no
idea what, for instance, is the difference between ASCII and UK.  I've
never seen a codepage or ISO definition for just "German" either.  What
would I use here for Unicode?  I see some listed in encoding.c
builtin_tabs; however, the code that uses it is not commented at all and
is quite confusing.  The use of "font" in both the code and the
documentation is confusing as well.

2) How does this all relate to the charset command?

3) Digging around, I see some clues and references to things like this
over at http://www.xfree86.org/current/ctlseqs.html; is that what this
means?  I do see GL/GR references in the DEC vt420 Programmer Reference
Manual.

This all still leaves me baffled.  I have never seen Unix applications
generate the ISO 2022/vt220 sequences to swap out character sets, and it
would be entirely superfluous in a Unicode context anyhow.  How do I
provide my own mapping from Unicode to the terminal?

Thanks!

John