Interface language and search language

Definition: Interface language is the language of a search engine's buttons, menus, and other display text. Search language can refer to the language of the query or the returned pages; a result-language filter selects languages for web results.

Key facts

As of 17 October 2026, the official documentation describes these controls:

• DuckDuckGo's URL parameter reference lists kl as Region under Result Settings, including ca-en for Canada and ca-fr for Canada (fr).
• Google's display-language help describes a preference for buttons and display text, separately from the language of search results.
• Google's Results Language Filter help provides a control for filtering web results to one or more preferred languages.
• Google's explanation of result languages identifies query language and location among the factors used to select result languages automatically.

What does DuckDuckGo's region parameter specify?

DuckDuckGo's parameter documentation allows settings to be added to a search URL. These examples keep the query unchanged and select different documented Canadian region options:

https://duckduckgo.com/?q=search&kl=ca-en
https://duckduckgo.com/?q=search&kl=ca-fr

The same table lists wt-wt for No region. Its label matters when recording a search: kl=ca-fr records the Canada (fr) region choice. The parameter reference does not document this control as an exclusive result-language filter.

How does Google separate display and result languages?

Google's display-language instructions define the interface preference through buttons and other display text. On Android, the Google app distinguishes the whole app's language, reached through Settings > Other Settings > App language, from the search-results page controls, reached through Settings > Language & region > Search language.

Google's result-language explanation says the language used for Google display text also helps it choose result languages. Query language, device language, and location contribute to that choice. A query can therefore return pages in a different language from the query itself. The display preference and the result filter remain separate settings even though display language contributes to automatic selection.

How can result languages be checked explicitly?

Google's filter instructions place the search-page control under Tools > Any language. On a computer, the saved preference is available through Search settings > Languages > Results Language Filter > Edit, followed by language selection and Confirm.

The same instructions explain that selecting several languages creates a combined filter. Their example selects French, Indonesian, and Arabic together. For a website visibility comparison, the selected language group should therefore be recorded alongside the query. Google also documents that filtering may fail for some search features or when a page's language cannot be detected.

Related terms

• How do DuckDuckGo region settings differ from language settings?
• HTML lang attribute
• AI answer reproducibility
• How should an agency compare answers across languages?

FAQ

Does choosing English for the interface restrict results to English?

Google's display-language help says changing the language of buttons and display text leaves the language of search results unchanged. You can use its separate result-language control to select preferred result languages.

Why might Google's language filter be missing?

Google's filter help says the Results Language Filter does not appear when English is the only selected language.

What value selects no region in DuckDuckGo?

DuckDuckGo's parameter reference lists kl=wt-wt for No region.

Sources

1. DuckDuckGo, "How To Use URL Parameters To Change Your DuckDuckGo Search Settings", undated
2. Google, "Change your display language on Google", undated
3. Google, "Use Results Language Filter for Google Search", undated
4. Google, "How Google knows what language to show in search results", undated

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