I'm thinking much more along the lines of cross-wiki user pages right now, which would require technology that would enable cross-wiki watchlists in the future. More information coming soon.
Cross-wiki userpages sounds like it would be largely unhelpful across sister projects (information relevant to one project is not that likely to be relevant to another), and pretty much impossible across languages (how would translation be done?), imo.
(Also pointing out that StructuredProfile would probably need some changes to work on certain projects. On Wiktionary, for example, "Interests" and "Languages" overlap enormously.)
Leaving the question of relevance of certain data for varying project wikis aside - having structured data makes translation a manageable task. Volunteers at translatewiki.net will be translating all prompts and all selecteable answers. Rendering software will be using these translations as appropriate. That's all.