In the upper right corner, to the left of your profile picture, click the menu button (the one with the three vertical dots).
The first choice on the menu overlay is Preferences. This time, you'll be directed to the User Preferences page.
The second item in the left-hand list, Language & Region, is visible. Click the following item.
The page where you can select your language, date, time, and number formats will appear. The Language drop-down menu is the first one on this page. From this list, pick the language you like.
Hit the Save button, the sole blue button on this page, after choosing your language.