Confluence uses user.language and user.country to choose default language

• Steps to reproduce the problem
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  1. Download and unpack confluence-2.2.9-std.zip to E:\confluence-2.2.9-std

2. Specify confluence.home in E:\confluence-2.2.9-std\confluence\WEB-INF\classes\confluence-init.properties as E:/confluence-2.2.9-std/data

3. Start server by calling E:\confluence-2.2.9-std\bin\startup.bat

4. Navigate browser to http://localhost:8080

5. Confluence Setup Wizard appears, paste in license key, choose Standard installation, created admin account, "start using confluence now"

6. Go to administration console, choose Languages, verify that only english is offered

7. Shut down server

8. Go to E:\confluence-2.2.9-std\languages

9. Open command line here and enter "ant -Dlanguage=de_DE install", press enter. The output reads as follows:

E:\confluence-2.2.9-std\languages>ant -Dlanguage=de_DE install
Buildfile: build.xml

checklanguage:

build:
[mkdir] Created dir: E:\confluence-2.2.9-std\languages\de_DE\classes
[mkdir] Created dir: E:\confluence-2.2.9-std\languages\de_DE\dist
[jar] Building jar: E:\confluence-2.2.9-std\languages\de_DE\dist\languages-de_DE.jar

install:
[copy] Copying 1 file to E:\confluence-2.2.9-std\confluence\WEB-INF\lib
[echo] macros-de_DE.jar installed - restart Confluence to use the language pack.

BUILD SUCCESSFUL
Total time: 0 seconds

10. Restart server with E:\confluence-2.2.9-std\bin\startup.bat

11. Point Firefox to http://localhost:8080 again, Login, Dashboard-Page appears in German

12. Choose Administration ("Leitung") from menu in upper right corner, "Administrationsplatz" appears, choose "Languages":
Deutsch (German) and English are offered, English is chosen as default (marked as such by a slightly grey background)
This is the error:
Confluence's UI should be displayed in English even after installing the german language plugin (step 9).
The UI should only be in German, when German had been selected as Confluence's default language, which isn't the case here.

13. Take a look at the log file E:\confluence-2.2.9-std\logs\atlassian-confluence.log and find the following line:
2006-11-16 19:49:03,546 WARN [atlassian.confluence.languages.DefaultLanguageManager] getLanguage Unable to find configured language module: null

• Workaround
  ^^^^^^^^^^
  Add the following text as line 43 into file E:\confluence-2.2.9-std\bin\catalina.bat:

 set JAVA_OPTS="-Duser.language=en -Duser.country=US"

Now, restart the server and navigate your browser to Confluence. The UI is now being displayed correctly in English.
No more warning message from [atlassian.confluence.languages.DefaultLanguageManager] in atlassian-confluence.log.
Changing confluence's default language from english to german and back works as desired.

Conclusion
^^^^^^^^^^
Confluence chooses its default UI language erroneously from the system default (Property user.language).
It should rather take it from its own configuration.