• a way to tell LaTeX to use "Figura" instead of "Figure" (and the like), use the correct hyphenation rules and language-specific typographic rules etc. (see e.g. https://en.wikibooks.org/wiki/LaTeX/Internationalization). To accomplish this, packages like babel (`\usepackage[brazilian]{babel}`) or polyglossia were created and already include their "dictionaries".
• a dictionary in Brazilian and written in LaTeX (of course you would like to see the source code and not only the resulting pdf): While I am not aware of any freely available `BrazilianDictionary.tex`, the multicol package could be useful (see also https://www.sharelatex.com/learn/Multiple_columns) as well as the thumbs package and of course hyperref for cross-referencing.