Mozilla Firefox has an option to display webpages in various different languages if those languages are supported by the given website. What this means is that if a website supports multiple languages (like a German website primarily displaying webpages in German language and also in English for international visitors, it can be useful to render pages like those in native language through this Firefox feature).
To do this :
Go to Tools > Options.
Next, under the Content tab, hit the “Choose” button for Languages.
Click the “Add” button and add languages of your choice from the drop-down menu that appears. The preference for added languages can be changed by moving them up or down the list. In the below example, webpages will be displayed in German if the accessed website supports that, else they would be shown in English.
All done. .