Who cares what language you use?
Your web site is written in Swedish, but hosted in Germany, and uses a international TLD. How do you tell all the search engines what they need to know about the language and targeted country for you site?
Unfortunately, as you probably guessed, All the major search engines deal with this issue slightly differently. Which means you, as a web manager, need to keep your fingers crossed even if you do follow the appropriate web standards.
Google ignores, for ranking purposes, most of the meta data tags on a web page, including the language meta tag. At the time of writing, Google only takes note of 7 specific meta tags.
If you have a country-neutral top level domain (such as .com) then you need to geo-target your website within Google webmaster tools.
Bing
In contrast to Google, Bing does use a number of meta tags when indexing pages.
One of those tags is the Content-language meta tag. Without a Content-language meta tag, Bing presumes that the geo-located IP address of your web-host provider is the country you are targeting your site towards. So if your site is hosted in a different country, you need the language meta tag to correct this.
Yahoo
Yahoo isn’t as straight talking as Google and Bing. They say they do look at the Content-language meta tag, but that they don’t always trust it. Which isn’t the most concrete answer to the question: How to Correct the Default Language Which Yahoo! Search Detects for Your Site.
Web standards
The best you can do as a web manager is to make sure that all of your pages follow three web standards: Doctype, <html> lang attribute, and the content-language meta tag. If all your pages make correct use of these components of your markup, then not only do you help certain search engines correctly assess the language of your content, but you also make your site more accessable to visitors using screen readers.
Doctype
Some people get confused about the doctype declaration at the very start of your markup. You should never change the language of the doctype to reflext the content of your page. The language indicated in the doctype declaration is always the language the DTD is written in.
Lang attribute
Setting the lang attribute of the <html> tag in your markup is important from an accessability and web standards viewpoint. It is, for example, the lang attribute that ensures that screen readers read your content in the correct language.
Remember to always add the lang attribute to any tags that surround content in your markup that differs in language from the language that you declared in the <html> tag.
Content-language Meta tag
Finnally, the language meta tag which Bing uses and Yahoo kind of uses. Make sure you place the meta tag in the <head> section of your page. Make sure you choose the correct ISO region and language combination.
Here is an example in XHTML for British English.
<meta http-equiv="content-language" content="en-gb" />