tlmgr update --all

[Karl Berry]

    >     perl: warning: Falling back to the standard locale ("C").
    Ahh that one ... I remember that.

It sounded familiar but I couldn't place it.

    $ luatex -ini   -jobname=luatex -progname=luatex luatex.ini
    Unable to read locale data: please check the 'locale' settings of
    your environment for consistency. Exiting now.
    
Yeah. Let me also restate Harald's messages:

    perl: warning: Setting locale failed.
    perl: warning: Please check that your locale settings:
            LANGUAGE = (unset),
            LC_ALL = (unset),
            LANG = "de_DE.UTF-8"
        are supported and installed on your system.
    perl: warning: Falling back to the standard locale ("C").

I figured the problem was ultimately LuaTeX-relatex, since those were
the only failing engines. But then why do the warning msgs explicitly
say "perl:"?  I guess because it's fmtutil. But it doesn't make sense to me.

    luatex is too ...... to work with broken locales 

And, what is wrong with "de_DE.UTF-8" for luatex? I'm sure Harald has
German installed on his system. But maybe not for luatex (or luahbtex)?
I don't know how to tell.

All these weird things are what made me pass it to you ... sorry.

    My tendency is to do it fmtutil just before the actual engine call,
    so that other error messages are still in the current language.

Sounds good to me. Could even do it only if the engine is luatex, but
I guess there's no practical difference/benefit to that. --thanks, karl.