In Fluid Topics, there are two types of languages:
By default, it is possible to navigate the interface in one language while browsing content in another.
In the following example, the interface is in French while the document opened in the Reader page is in English:
When modifying the interface language for the first time, the content language matches it (if possible). After modifying the interface language a second time, the two languages are independent unless an administrator enables language matching.