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
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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.