This article explains how to change the language on Twitter (PC or Mac).
Steps

Step 1. Open the browser of your choice (Safari, Chrome or Firefox) and go to
If you are not logged in, enter your username and password

Step 2. Click on the circle that contains your profile picture:
is located at the top right.

Step 3. Select Settings and privacy

Step 4. Select a language from the drop-down menu
This menu is located next to "Language" and shows the current one. Click on it, then select a new language from the options.

Step 5. Scroll down and click Save Changes at the bottom of the screen
A pop-up window will appear.

Step 6. Retype the password:
it is a necessary step for security reasons.