de_DE has been using the wrong group separator for over 18 years

[kdex]

To give some context: I have previously posted the following on libc-locales 
and was asked to bring this to the attention of senior developers on this 
least who speak German.

I have noticed that the locale `de_DE` has erroneously been using a full stop 
(U+002E) for the thousands (group) separator in `mon_thousands_sep` and 
`thousands_sep` ever since 2000. The usage of a full stop to group thousands 
has (to my knowledge) has never been standardized.

As per DIN 1333, DIN 5008, and DIN EN ISO 80000, the separator should have 
been a thin space (U+2009).

In fact, DIN 1333 even explicitly forbids the usage of U+002E to group 
thousands, and DIN EN ISO 80000 explicitly excludes all other characters than 
a thin space.

Has anyone noticed this before? I fear that this change might break a lot of 
code that relies on the separator being wrong. Yet, this really should be 
fixed…

What's the best way to deal with this?

For further information, please also refer to the relevant section on 
Wikipedia at [1] (German).

[1] https://de.wikipedia.org/wiki/
Zifferngruppierung#Zur_Problematik_von_Punkt_und_Komma_f%C3%BCr_Tausender-
_und_Dezimaltrennzeichen
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