You have two options:
1. In the Login Form you can select the language version
After selecting the version, the language version of the form will change and after logging in, the interface will also be in the selected language version. The selection will be saved in your profile.
2. Edit your own profile
- Select on the top-right menu on the avatar/first name and choose Edit profile
- In edit form, change language and click Save (you will be logged out, read why)