Miraheze provides imports for all wikis. To request an import please create a Phabricator task with a title of 'Import for [your wikis name]' replacing the name with a link to your wiki and attaching an XML dump. If it is a private wiki you can send this by email to staffmiraheze.org .
Imports are done by the System administrators. They are done using the importDump.php and importImages.php maintenance scripts. The duration of the import depends on the size of the wiki.