I noticed JavaScript errors on the issue page when using the german locale. The FireFox JavaScript Console shows the problem:

initPinComments('Immer anzeigen',
'Immer 'Kommentar hinzufügen' Bereich anzeigen',
'Zunächst ausblenden',
''Kommentar hinzufügen' Bereich zunächst ausblenden');

The same code from jira.atlassian.com looks like this:

initPinComments('Always show',
'Always show add comment area',
'Initially hide',
'Initially hide comment area');

The problem is obviously some unencoded quotes. I could probably fix this by modifying the language properties, however it is a general problem: the contents of the language properties files must be properly encoded in any location.