I've just read through this thread for the first time and see that you are in the process of updating the mod (as of last October).
There are a couple of comments I had from the old posts, which you may already be addressing, but I'll mention them here just in case they help.

You discussed providing pre-edited language files versus giving instructions for adding defines to them. I think it would be simpler and safer all around to add new files for the mod's defines (in the /extra_definitions/ folder), rather than either of the above. Also, moving all output text to language define files as you mentioned is definitely the way to go.

The fix for db table prefixes:
$result = $db->Execute("SELECT * FROM (DB_PREFIX . 'events') WHERE (EndDate >= NOW()-1) ORDER BY StartDate");
might better be done in the ZC standard way, by defining TABLE_EVENTS in a new (extra_datafiles) file and using that. This would even allow the user to change the table's name if they want to, without getting deep into the PHP code.
$result = $db->Execute("SELECT * FROM " . TABLE_EVENTS . " WHERE (EndDate >= NOW()-1) ORDER BY StartDate");