When an Optimizely Search & Navigation index is set up, you define its supported languages. 

When setting up an index, you define its supported languages, see [Architecture](🔗) for a complete list of languages. When searching a defined language, you use the `Client` class and the `Search` extension method, and pass to the `Search` extension method an instance of the `Language` class.

Optimizely Search & Navigation also has a [Language routing](🔗) feature that lets you limit search queries to documents in a specified language.

An instance for each supported language is exposed as a static property on the `Language` class.

The language parameter only applies when specifying one or more fields to search. If you do not select fields, the search is made over the special **\_all** field, which supports only a single analyzer. Likewise, the standard analyzer is used when searching attachments (Word documents, PDFs, and so on).

Result of adding a language parameter: If you specify a language, the search uses _stemming_adapted for that language. In such a case, results are returned in all languages \_and_ for stemmed words in the specified language. To limit results to a specific language, use a [filter](🔗) (for example, FilterForVisitor).