I am starting to think that filter may not be the best way to translate content. It was widely used though and was recommend a few times in these forums.
While trying to find the bbPress string swap plugin that was a bbPress plugin that use to do this exact thing fine. I came upon this that lead me to find the alternative to the gettext filter and using global $l10n;
https://github.com/justintadlock/hybrid-core/issues/49
Here is an example with BuddyPress and I am sure there is a way to make this kind of thing work with bbPress.
