There are different places where you would enter translations depending on what you want. If you want global translations, that would probably go on the data dictionary. If you want different translations for a system code, you could do a jargon override by system in the data dictionary. If you want something only on a specific application or UBE, you could do a vocabulary override on the APPL/UBE. Try searching Oracle for document "Translation Tools Guide".
Your screen shot is for Vocabulary Overrides for a specific UBE. Note at the top, Language defaults to blank - Domestic Language. When you look at the grid, you see all of the different translatable elements in the UBE. The Override column tells you whether or not the element already has an override. Most do in your screen shot (ie. the UBE is overriding the default data dictionary value).
To see translations for a different language, enter the language code at the top and click Find.