The feeds such as /comments/feed do not work when using a localized copy of wordpress.
This is due to them putting in the « and other entities that are taken from the gettext .po resource files.
For example ru_RU is totally hosed, and it's because the strings files put in » and « and those are then put into the XML, and it results in invalid XML/invalid feed.
Suggestion: either scrub the gettext results, or tell everyone to put normal quotes in their stuff (or numeric entities), or don't use those strings inside of the feeds...
This is how it comes out:
`<title>Comment on post «Post title» by user</title>'
That breaks the feeds.