Here you can select the language and then keyboard layout within each language section. If it does not appear in this list, click the ⋮ button. This will enable you to search for the keyboard layout you wish to use.
After choosing the keyboard layout, click Done. You will be brought back to the following dialog with your new keyboard layout. In the image below, we are now using English (US), Finnish, and Swedish layout.
You can remove a keyboard layout by click on one of the items, for instance Swedish, then clicking the `-` button.
If you wish to use multiple keyboard layouts, you can switch to them by using: `Windows key + Space` or by adding the Keyboard Layout Indicator applet to your Budgie panel.