For the example of /activity, you need to make the change in a few places. Make sure you're using your text editor in UTF-8 mode, and edit the bold phrases below:
'nav_activity' => 'activity',
'activity' => QA_INCLUDE_DIR.'qa-page-home.php',
'url' => qa_path_html('activity'),
Similar logic applies for the other URLs, except some don't have an entry in qa-page-home.php. In general I'd recommend doing a full text search across the code base for the relevant word, and then trying to understand the PHP context to decide whether or not the substitution is necessary.