Xinput broken for C and ISO-8859 locales

xinput only seems to work properly when using UTF8 locales. It does NOT work properly with the default locale ©, en_GB.ISO-8858-1 and en_GB.ISO-8858-15 locales.
Is there some magic to make the C locale and ISO-8858 locales work ?
At the very least the default locale © should always work properly.
For various reasons I which to use a Latin character set (ISO-8858-1, ISO-8859-9 or ISO-8859-15) and a British(en_GB) or C locale so it is a pain when these don’t work properly.

Hi @Mark,

does this help?:

Have you done a full system update?: