Are you looking for some way to export fields from a site with ACF 4 so that you can use them in ACF 5? Or just for use in ACF 4 for creating fields in code?
For either one of these, while I’m not the developer, I can say that this will probably not happen. ACF 4 is no longer in active development and the only work done on it are security fixes and to make sure it keeps working with the latest version of WP. The developer has plans to eventually replace the version in the WP repo with a version of ACF 5, but I don’t know where that’s at.
In either of the cases I would suggest looking at @morgan‘s suggestion.
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