Question: we need to translate twice the labels? Once for v9, once for master?
answer: you don't need to translate both branches, if you take a look at https://crowdin.com/project/typo3-cms/fr and hover over the blue bar of 9.5 those are only 4000 words while the master are in total 53k words, so in 9.5 there is only stuff which is not in master.
you could translate those if different but not required (bearbeitet)
Question: we need to translate twice the labels? Once for v9, once for master?
answer: you don't need to translate both branches, if you take a look at https://crowdin.com/project/typo3-cms/fr and hover over the blue bar of 9.5 those are only 4000 words while the master are in total 53k words, so in 9.5 there is only stuff which is not in master. you could translate those if different but not required (bearbeitet)