Thailand's currency in difficulty (7)
I believe the answer is:
trouble
'difficulty' is the definition.
(trouble can mean a difficult situation)
'thailand's currency' is the wordplay.
'thailand' becomes 'T' (abbreviation on car registration plates).
'currency' becomes 'rouble' (Russian rouble).
't'+'rouble'='TROUBLE'
'in' is the link.
(Other definitions for trouble that I've seen before include "'Care, distress (7)'" , "Jam" , "Effort - (cause of) worry" , "'A... shared is a... halved'" , "Difficulty, problems" .)