It’s probably just some Czech comments - just ignore these lines.

The Bat! is an e-mail client (like Outlook, Thunderbird, Eudora, …)
avast! for The Bat! is an avast! plugin for this program.

I’d say “Page” and “of”. The specifiers %s will be replaced by some numbers - so it will say “Page 2 of 5” (for example).

No, it’s just formatting HTML tags.

In what context? I.e. where exactly is it used?