Problem

The only encoding that Confluence support is UTF-8
However, admins may change this setting in General Configuration > Formatting and International Settings
Setting Confluence default encoding to UTF-16 from this page will renders 'chinese' characters for spaces and even the login screen.
It is also impossible to set it back to UTF-8, since the UI is not rendered

To verify this is the problem run in the database:

SELECT BANDANAVALUE FROM BANDANA where BANDANAKEY = 'atlassian.confluence.settings';

if it returns a different value of UTF-8 in the result, then it is affected.

Steps to reproduce:

1. Set up a new Confluence
2. Go under the Administrator Panel > General Configuration > Formatting and International Settings and change Encoding field from UTF-8 to UTF-16.

Expected Result:
Confluence doesn't allow the change

Actual Result:
Confluence becomes unusable, styles are broken and administration sections are locked.
Can't be reverted back unless a DB change is done.

Workaround

1. Shut down Confluence and perform a database backup
2. Run:

   UPDATE  BANDANA set BANDANAVALUE = REPLACE(BANDANAVALUE, 'UTF-16', 'UTF-8') where BANDANAKEY = 'atlassian.confluence.settings';
   

3. Start Confluence