acf_form in a German frontend with v5.6.10 of ACF Pro and it works perfectly. Great tech! If the required fields are not completed, the error message Überprüfung fehlgeschlagen. Für 16 Felder ist eine Aktualisierung notwendig appears at the top of the form. All good.
However, despite all translations being available, this text appears in English if I update to v5.7.x.
The entire JS api was replaced in 5.7.*, more than likely this got missed. You should submit this to support by contacting them here https://www.advancedcustomfields.com/contact/
Have sent the link to this ticket. Thanks John.
Moving the call to
wp_head fixed the issue. Thanks Elliot.
This still appears to be a problem. If I add the call to
acf_form_head using the
wp_head hook, the main error message _Validation failed. 1 field requires attention_ still appears in English. I found that my moving it to the
wp action, which is called before
wp_head, the problem is solved.