I have no experience with the Forms tab in the Archetype Designer, but this problem may well have the same root cause as the behaviour we observed in the opt and Web templates generated from multilingual templates:
If we used an archetype multiple times within a template, the DE and FR translations in the opt and Web templates (when EN was selected as the primary language) would only reflect the node name, description and comment of an archetype’s first occurrence in the template for each other instance of the same archetype. The specific node names, descriptions and comments for subsequent occurrences of the same archetype were simply missing entirely from the opt and Web templates.
We described our problem in Translations lost in OPT when an archetype is used multiple times and Ian McNicoll answered that this problem stems from the definition of ADL1.4 and the opt, and that it would only be resolved by ADL2 and opt2.
@Silje, thank you very much for pointing out this thread and, in doing so, highlighting the workaround using the annotation ‘L10n’. I was not aware of this until now.