This page is for setting up the languages you want to use and to be associated with the current profile.
The "UI Language" field is for selecting your native language, or the language you want this website to use for menu items, labels, messages, etc.
The "Host Languages" field is for selecting the language the lessons will use to explain things. It typically is your native language, but if lessons don't support your native language, you can choose a different language you might also know, or have multiple languages.
The "Target Languages" field is for selecting the languages you want to study. It might include alternate forms of the language you want to study, such as a romanization, or it might include entirely different languages, allowing you to compare and contrast, if the lesson supports the languages.
Add additional languages via the extra drop down menus showing the "(add language here)" selection.
Remove languages by selecting the "(remove)" item in the drop down menu item lists.
Go to the "Profile" page to select or edit profiles. Profiles allow you to set up different language configurations and more easily switch between them.
Don't see the language you are interested in? If you are registered as a teacher, you can add languages via the Teacher->Languages page. By default, JTLanguage supports the languages supported by Google Translate. But note that just because a language is listed, it doesn't mean that there is any content for it. You might need to kick it off with adding it yourself, by creating your own courses, or by adding translations to exisitng courses.