I am trying to: Translate a ACF text field within a ACF Flexible content block, it keeps getting the Dutch translation. If adding a textfield to the same flexible block it is not saving at all. See it seems to keep the default input after saving.
Link to a page where the issue can be seen: hidden link
I expected to see: a French translation where "Onze flexibele wandoplossingen" is located
First, I note that you are not using the recently released version 2.0 of ACFML. In terms of taking advantage of the new default settings that wouldn't apply to your existing field groups, for which you would use Expert mode that gives you full manual control.
I mention that, because if you refer to the ACFML documentation, it has now been updated to match version 2.0.
(If you want to update—take a backup before you do—go to the custom installer page you can reach via the registered link of any of the WPML plugins listed on the plugins page and click the "Check for updates" button if the update to 2.0 is not shown.)
