Many of our goodfaith editors are actually visitors from other wikis, some of our badfaith editors are also. If we are coding something like this it would be cool to have an option that automatically replicated your userpage or at least a link to it when you first edited on a project.
Topic on Talk:GlobalProfile/design
I think my ideal implementation for this would be to have all the data stored centrally on a cross-wiki server (data.mediawiki.org, maybe) so that your profile will be accessible on every wiki that you have unified. This will help alleviate the problem you're describing.
That risks increasing the amount of foreign language userpages on wikis. Better I would suggest to have a userpage per language - this would be more easily be done if Wikinews, wikiquote wiktionary etc etc were all views of one wiki and we moved towards one wiki per language.
Multilingual Wikimedians tend to have their different userpages in the appropriate languages, and they are most likely to be active cross wiki
If the user has a central user page, he can use
{{#switch:{{CONTENTLANGUAGE}}
|fr = User page in French
|pt = User page in Portuguese
|en|#default = User page in English
}}
to get it displayed differently depending on the wiki's language code.