Come first in French, which is hard to pick up (6)
I believe the answer is:
leaden
'is hard to pick up' is the definition.
(I've seen this in another clue)
'come first in french' is the wordplay.
I cannot quite see how this works, but
'first' could be 'lead' (lead can mean leading or primary) and 'lead' is located in the answer.
'in french' could be 'en' (French word for 'in') and 'en' is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'which' is the link.
Can you help me to learn more?
(Other definitions for leaden that I've seen before include "Heavy - plodding" , "Gloomy - slow-moving" , "Heavy or slow, like dark-gray metal" , "Leaned over in slow, heavy way" , "Heavy - overcast" .)