Problem:
A site with a huge amount of content is using the Translate everything mode and appears to be stuck on "WPML preparing content for translation"
Solution:
Make sure that the site uses a WP Memory Limit of at least 256M.
The current values and memory usage are visible at WPML > Support > WordPress.
Then, also please adjust the PHP max_execution_time to a high value, which in this case made the tasks complete faster.
Also, take note, that creating new translation jobs at WPML > Translation Management > Dashboard will send the jobs directly to translation again, which can be used as a workaround if it seems to you that some contents remain stuck inside the queue.
