There're couple problems with notification emails.

1. Seems to me there's a problem with notifications algorithm itself. For example, if someone subscribes to question in category X, then on that category itself and then on all categories, sometimes he can get a bunch of emails: new answer in question, new answer in category etc. I can't figure out some patterns, but sometimes it works properly, sometimes sends extra emails. I even looked in mail queue in CJ Lib and saw double emails.

For example, subscribe to all categories, then to one selected category and try to add a question to it. You'll get 2 emails: one global, one for category.

2. If you put HTML entities in subject string (like this: "My site") they won't be processed and you get the same "My site" line in email subject.

3. Looks like there's a problem with this line:

EMAIL_USER_ANSWER_APPROVED_SUB="Your answer, submitted on %1$s, is approved."

%1$s here is being changed to username, not site name. Looks like a bug. Moreover, I think question title should be here since there's similar line for question approval.
4. There're also some unclosed or improperly closed tags in language lines like this:

EMAIL_QUESTION_APPROVAL_BODY="<p>Hi Administrator, </p><p>A new question is submitted by <strong>%1$s</strong> and is pending approval by you. Please find below the details.</p><div><strong>Title:</strong> %2$s</div><div><strong>Description:</strong> %3$s</div><div><strong>Attachments:</strong> %4$s</div><p>%5$s - %6$s</p><p>Thank you." <-- No closing tag!

But that's not a big deal. It's just me being picky :-)