Legislation limiting Belgium’s currency (5)
I believe the answer is:
ruble
'currency' is the definition.
(I have seen 'Russian currency ' mean 'ruble' so perhaps 'currency' could also mean 'ruble')
'legislation limiting belgium's' is the wordplay.
'legislation' becomes 'rule'.
'limiting' indicates putting letters inside.
'belgium' becomes 'b' (international vehicle registration code).
'rule' enclosing 'b' is 'RUBLE'.
(Other definitions for ruble that I've seen before include "Russian currency" , "ready in Russia" , "Unit of money in Russia" .)