example:

CMS page in dutch

page has contentarea with 'local' blocks, each block has  their own contentareas with more 'local' blocks.

select another language in language gadget that doesn't exist yet.

select hamburger menu for that new language: replace content\duplicate content -> choose source language dutch

all blocks are correctly copied from the dutch language page, but the language inside the blocks is not duplicated.

I still have to go to each block (recursively), select edit hamburger menu on the block and perform replace content\duplicate content in language gadget for each block