Installation directory contains special characters, please remove them and try again.

No it doesn't.

What I am attempting to do; install PHPBB3 via install central to a sub folder of a sub folder.

Example; Website root domain automatically forwards users to a sub directory where the site actually is. www.website.com/en so the forum would be at www.website.com/en/forum

apparently it reads 'en/forum' as a folder rather than two seperate folders. Manual install is necessary I suppose. Still really annoying.