I am a big fan of multi-language sites. And I think this implementation would be stellar.
...just not for SE.
I see three major issues with this implementation:
- Translated questions/answers aren't vetted by the community
- The value of having a translated version isn't apparent
- Maintenance becomes a nightmare
If this implemented, I think it should be done in a different way/format.
So there's this super highly viewed question. There are over a million views on that sucker, and 35 answers. Right now the question 'works' because the voting indicates which answers are most useful. If you translate that, suddenly you have a mess of 35 different answers to what (appears to be) a very straightforward question.
So if you translate this question on to another site, how do you decide which answers to translate? If you translate them all, there is a mess of answers with no indication of which is going to be helpful (which negates the concept of SE as a repository of answers to questions without having to sort through the chaff). If you translate only some, what happens if the library/language/version has been changed and a newer answer is actually better than the old highly voted ones? You lose valuable signal. While comments should always be edited in to the post, there is a chance that a comment makes the answer useful in the end.
What is the Value of Translating Content?
Most questions/answers are not canonical. What is the value of translating this question for instance? At least the previous question about checking if a checkbox is checked has a lot of widespread appeal -- this one is likely to be useless to a majority of people (and how would you even find it in the first place?).
The same applies to linking to similar questions. If I see a Portuguese version of that question, would it really be of any benefit to link the two together? I could see this being an added layer of frustration where you go to a question, see no answer in your language, go to the linked question in a foreign language and find it no more useful than the one you were just reading.
Without some way of ensuring the linking/translating the content provides added value, creating an incentive to do it (through badges or otherwise) will add more noise rather than more signal.
Not to mention that maintenance becomes a nightmare. If I translate/link a question, and then one of the languages gets a substantial edit or update, what do we do with the other? What happens if one gets closed? What happens if the answers on the two are dramatically different? What happens if the authors of each end up having different problems, or selecting different answers?
SO has enough trouble maintaining the content in English alone due to volume. By increasing the amount of content by including other languages, while reducing the capabilities to maintain it by restricting that maintenance to bilingual folk, the problem would just be made worse. Any suggestion that deals with multiple languages should have some pretty fancy tools included to make maintenance far less painless than it would be with the current methods of maintaining info.
If you see good content on SO that isn't available on Portuguese.SO, then go ahead and create a self-answered question sharing that content. Make sure the translation matches all the important keywords, properly attribute the post, and then you've worked to make that content available in another language.
If you see content that is related, feel free to link that in a comment. Giving people the ability to find (and voluntarily translate) answers may be useful, but doesn't need a special feature.
Good content will always float to the top. You have the tools available already to link things back and forth. If there is added value (demonstrated through manual tinkering with the tools provided), then you may have a much stronger case for implementation in the future. And you will probably get much better ideas about what works, what doesn't, and how to make the implementation easier based on actual experience doing it.