Once you've navigated to 🌐 Translation...
Start by clicking on Edit Origin
Origin refers to the language you will be translating from. Let's say we want to translate from a French phrase into German. In this example, French would be our Origin Language. Clicking on Edit Origin will bring up languages supported on Bittranslate.
Simply click on "🇫🇷 FR" to select French
As you can see, the origin language now reads "🇫🇷 FR" instead of "🏴 EN"
Now, click on Edit Destination
Completing the airport analogy, Destination refers to the language you wish to translate to. From our French to German example, German would be our Destination language. Clicking on Edit Destination will pull up a very similar menu to Edit Origin.
Finally, click on "🇩🇪 DE" to select German
And we're all set! The origin language has been set to French and the destination language set to German. See the next guide on how to translate.