How to fix "en_DE.UTF-8" (locales) warnings? [duplicate]

Solution 1:

Ok, here is what I assume:

I set up KDE to use the english (en) language but german (DE) formats, therefore it tries to set my locale to a combination of both: en_DE.
Like any british user would get en_UK and someone from New Zealand en_NZ.
But unfortunately noone(?) ever(?) created a locale definition for my combination: en_DE.

So all the warnings are correct and simple say, that there isn't a locale en_DE on my system and it can't be found anywhere.
After getting this insight by some googling, I made sure all necessary(?) locales are installed on my system:

sudo locale-gen en_US en_US.UTF-8 de_DE de_DE.UTF-8 

And defined that, en_DE.UTF-8 should use the same locale definition as de_DE:

sudo localedef -i de_DE -f UTF-8 en_DE.UTF-8

A subsequent sudo dpkg-reconfigure locales did no longer produce any warnings/errors and I hope, that I have fixed this annoyance.

As I mentioned in my question, I don't understand/grok the problem fully and didn't read any man pages or other official resources about locales (shame on me and I should go rtfm), so I don't know, if I really fixed my problem and didn't introduce some new by this questionable localedef call.

Hopefully someone will enlighten me and/or point the corresponding fine manual.
At least I hope, this answer help some others, who have also this strange locale en_DE and googling didn't help within the first results.