Hi Sebastien,
There is no technical possibility for both storing the translation history of the Theme translations and bringing them back in a bulk, to my regret.
Once the translations are are done you may export them to have a backup (Langshop>Translations>Themes>Storefront elements>More actions>Export).
Should you have any other questions please contact us via LiveChat or email support@langshop.app.
Have a good one!
Best regards,
Langshop team