[ColinHowell]

Originally Posted by Koir

In the sentence context, "not to mention" is used in a way to bring emphasis to the concept that comes after it (continued success) and link it to the previous concept (reason JapanForum was created). This way, it creates a sense of time for the reader connecting the past to the future.

This is one of those English figures of speech which must be quite confusing for non-native speakers. Saying "... X, not to mention Y" is actually a way of stating that Y applies even more strongly to the subject than X does. Other forms with the same effect are "... X, much less Y", "... X, let alone Y", and "... X, to say nothing of Y".

I think most native English speakers use these expressions automatically to achieve this effect, without thinking about the literal meaning of the words used. Since I never think about it either, answering this question was rather difficult for me.

I found out that these expressions all come from an old technique of rhetoric (called paralipsis), in which the speaker calls attention to something by pretending not to mention it. I knew nothing about the origins of this before looking up these phrases to answer YuriTokoro's puzzlement, so even we experienced English speakers can definitely learn something here.