For years 500 words per minute (approximately one printed page per minute) has been my baseline speed for most of the material I read in English. I read slower in my second languages, of course. Back in my college days, when I wanted to make sure I wasn't being slowed down in my studies by a too-slow reading speed, I read a lot of books from the university library about reading skill improvement, and several jointly suggested that improving vocabulary improves reading speed. I took a course about English vocabulary based on Latin and Greek word roots, and that did seem to help for years afterward in both reading speed and reading comprehension.
[1] http://readinginthebrain.pagesperso-orange.fr/intro.htm
AFTER EDIT, TO REPLY TO QUESTION:
In this context, "second languages" is a quite normal designation for language(s) acquired after one's native language(s) were acquired. My user profile lists most of mine. I read best in Chinese and in German, besides English.