error: Invalid range end:

[Duncan Moore]

Some months ago I had what looks like the same issue with gawk 5.0.0 on
RISC OS, using a single byte Latin-1 locale. I traced it back as far as
character 255 (small letter Y with diaeresis), which has toupper(255) =
'Y', since there's no exact upper case equivalent in the character set.
From memory, gawk was doing some case insensitive initialisation, even
if it wasn't needed, and this caused the error.

At the time, I decided there's probably something screwy with the RISC
OS locale, like not satisfying some collation/toupper()/tolower()
constraints. But maybe there's a wider issue here. I worked
around/hacked it by remapping toupper(255) = 255 in the gawk source,
which is, I think, what other similar locales use.

It also affected other utilities, like grep, sed and find when regexps
are used case insensitively.

Duncan Moore