It's possible to translate pages into other languages thanks to the Translate Extension.
To translate a page, you need to have an account and to be logged in.
How to check what pages need to be translated
To see what pages need to be translated, go to the Language statistics page, enter the language code, and press enter.
The complete list of language codes can be found on the Translation statistics page.
How to translate a page
Go to the page itself, and at the top of the page, click on "Translate this page".
Select the language, enable the "Show untranslated messages" checkbox, and click on "Fetch".
In the first column of the table, click on the first line to translate.
Translate the message and click on "Save and open next". Repeat this step until all messages are translated.