Prolific in French, occasionally and in German (6)

I believe the answer is:

fecund

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'prolific' is the definition.
(synonyms)

'french occasionally and in german' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'and' says to put letters next to each other.
'in german' becomes 'und' (I can't justify this - if you can you should believe this answer much more).
The alternate letters of 'french' are 'fec'.
'fec'+'und'='FECUND'

'in' acts as a link.

Can you help me to learn more?

(Other definitions for fecund that I've seen before include "Highly productive" , "Producing many offspring or ideas" , "Prolific, fertile" , "Highly fertile" , "Fertile or productive" .)

I've seen this clue in The Guardian.

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