Does metadata and content have to be the...

Metadata on a page should reflect the actual page as much as possible, including being the same language.  Remember the Description element of the metadata is what is defaulted to show as the description on the page in the SERPS (search engine results pages).  You want this information to give a search user the most accurate idea of what is on the actual page as possible.  Overall ranking benefit of meta-information these days in Google are minimal, but Yahoo and MSN still give it some weight .  Metadata for each page should be relatively unique and targeted to the specific search term or "long tail" search term that is supported by the page's content.

I get a situation like these one with one of my french website : Most of targeted keywords (and so metadata area) from the content were english-term (eg. like "social-networking" as much used in the original english expression thant the "frenchie" translation...) and so we decided to use our metadata in english to rank well on the topics.

The content from page was in french, and we didn't suspect any wrong result on the ranking, maybe because we used the meta Lang "FR", and also <meta name="ROBOTS" content="NOODP, NOYDIR" /> to force a french snippet from ou meta description. Most of search engine did properly understand that in SERPs.

If your case is the same you can easily go for the same strategy ;-)

I have a similar issue with Hebrew websites, which have the additional issue of being a right-to-left language. We always use Hebrew metadata for the Hebrew pages and English metadata for the English pages, even on the same site.

Most surfers looking for Hebrew pages use google.co.il (the Hebrew language version of Google), they are looking for Hebrew terms and they are probably not going to click on a result with an English description. The English pages of these sites are aimed at an English (or at least non-Hebrew) audience, so there's no sense in putting Hebrew metadata.

So, whether the search engines give you credit or not may not be the most important thing to think about. My feeling is that when it comes to language, you need to focus on the people side of things.