Clicking on the Preferences link in the upper right while logged brings you to the User profile options of the preferences. In the Internationalisation section, a preferred language may be selected from a dropdown list. Setting this language will show all fixed text (labels) of the wiki in the requested language. As an example, the labels of the search box will be translated.
Not trying to change the menu language in the website?
This article is about changing the display Language for the MediaWiki interface that powers the Gramps wiki, not about the internationalization of Gramps itself nor the articles on Gramps features.
To explore a list of languages that have translated wiki pages documenting Gramps features, see the User Manual translations page. For other questions about Internationalization & Gramps, see the Gramps Language Policy.
Naturally, the content of the articles remains unchanged. Some articles have been translated and have a language bar at the bottom of the page to change the language of the article.