Go to Settings > Date & Time > Clock and check "Use a 24 hour clock". That should take care of that issue.
For the language, go to Settings > Language & Text and change that in two areas:
1. Under "Region", set your region and customize as desired.
2. Under "Language", drag the languages in the order you prefer.
Thank you so much for your answer. But you may have misunderstood my question. I mean the time format on the login window but not inside the system after logged in. The setting before login should be quite complicated, I guess maybe I should use terminal to do this.
Do you have other suggestion?
Thank you so much!
I'm sorry, I forgot one thing on the line I gave :
sudo defaults write /Library/Preferences/.GlobalPreferences AppleLocale "xx_XX"
is the correct one.
If the code "de_AT" (for Austria I guess) dosen't work, try with de_DE which I'm sure that OS X understand.
Sorry for the mistake.
Edit : I just try with "de_AT" on my own macbook pro, and it works fine. It will on your, by using the correct command line .