You can't add more language pairs. After creating an account on Fairlingo, you can translate to your native language from one source language. It's not possible to change your chosen native language, so make sure you select the right one. You can change your source language.
Changing the source language
1: Log in and go to profile & settings (figure 1)
2: Click on profile and delete your translation skills (figure 2)
3: Add the new source language (figure 3)
4: You will receive notifications for assignments in the language pair you added to your profile.
Keep in mind that you will loose your points if you change your source language. If you change back to a language you have worked in before, you will not get those points back.