A ruler can set out to follow up very popular speech (10)
I believe the answer is:
'popular speech' is the definition.
(speech used by ordinary people)
'a ruler can set out to follow up very' is the wordplay.
'set out' indicates an anagram.
'to follow' is a charade indicator (letters next to each other).
'up very' becomes 'v' (abbreviation. I am not sure about the 'up' bit.).
'arulercan' anagrammed gives 'ernacular'.
'ernacular' put after 'v' is 'VERNACULAR'.
Can you help me to learn more?
(Other definitions for vernacular that I've seen before include "Local-style" , "Characteristic language" , "Native tongue - dialect" , "Everyday language" , "Native language" .)