"Translation" in Settings allows you to manage a Preset's translation-related settings, such as desired target languages, in-line translation, and translation service providers.
(1) Select the default language pair
Source language: Select the default language you want to look up as Souce language. If you only care about the language you are translating to, you can set Source language as Auto Detect.
Target language: the language that displays the meaning/translation. This can be the language you're learning.
(2) Translation Providers
Choose your prefered translation provider: Google / Microsoft. This will be applied for the Popup Advanced Translate - Translate text)
(3) Inline translation:
Enable or disable inline translation. Read here if you don't know what it is.
If you want to change the source and/or target languages later, you can go to Dropdown and change it from there. Remember to pay attention to the Preset you're applying the change to.
Read more about how to quickly change things around in Dropdown here.