I think 'cmid' is Client Machine ID as used in MS Windows
Thisdirectionvertical 'btt' is 'bottom to top' as explained in langconfig documentation
'hook' is explained in the wikipedia
In reply to German Valero
Er: Re: Clarification needed for some English strings
In Moodle, cmid is the ID in course module table (the table that gathers all the elements in a course). Anyway, I think it should be translated literally.