How will the Polish mapywig site and the English mapywig site differ?
We will do our best to provide the same maps on both sites. Most of the supporting material will be the same. (Exceptions: Such documentation as a guide to Polish map terms for English speakers need not appear on the Polish site.) User contributions such as Forum and Shoutbox postings, etc. will naturally vary.   As our very limited time permits, we might transfer and translate items posted by users on one site to the other, but we can make no guarantees. If you want to reach users of both sites,  it would be best for you to post to both.

What about site membership?
Members of the Polish site are automatically members of the English site, and vice-versa.