fb:locale

The debug tool can definitely be off with their warnings. If it's reading it properly, I'd let it rest at that.

We'll look into setting the local parameter automatically in the future. Multi-lingual is something, in general, that we're aware we need to improve on. We do some things right, but in other areas we're lacking.

Thanks for the report. Hadn't seen that warning before, and we hate warnings there because people always ask about them

There's always inconsistencies in the Facebook documentation. There's never really a way to tell the situation either. Obviously, the code is always right, since that's how it works right now. The documentation can either be out of date, or an indicator of the future... and in this case, I don't know the answer

I would recommend fb:locale as that sounds correct. fb:locale:alternate sounds like something that can be specified in addition to locale, but really don't know the answer.

Hope this... helps.