If Foo and Bar are to represent similar content in different languages the it is assumed they will share a commmon reference (mostly the page name of the main content e.e.g Lorem ipsum) making those assignment link to each other through the sitelink navigation.
Interwiki annotation
In cases where an interwiki language link (e.g [[en:Foo]]) is added to a page (representing a non-local link, see also wgInterwikiMagic or wgExtraInterlanguageLinkPrefixes), SIL will create an additional Has interlanguage links entry (internally being identified by something like Foo::iwl.en).
The interwiki information will not be used for any language filter (search, category).
interlanguagelist
The parser function {{interlanguagelist: interlanguage reference | template }} can generate a customizable language target link list for the provided interlanguage reference and being formatted using a template with parameters:
target-linkbeing the target linklang-codethe language codelang-namerepresenting the localized language name for the language code#contains the list position
Using Template:InterlanguageLinksTemplate in interlanguagelist will output all available links to the Lorem ipsum reference on top of the page FooBar.
annotatedlanguage
The parser function is called either as {{annotatedlanguage: }} where it just returns the language code for the current page (if one is annotated using SIL) or with {{annotatedlanguage: template }} to return content as formatted using a template with parameters defined as:
target-linkbeing the target linklang-codethe language codelang-namerepresenting the localized language name for the language code
