WebTranslateIt Software SL/WebTranslateIt

Command Line Interface is a terminal window. See https://en.wikipedia.org/wiki/Command-line_interface

i18n_viz is the name of a plugin someone made to connect with WebTranslateIt

node.js and express.js are some kinds of programming languages

i18next is the name of a plugin someone made for WebTranslateIt

A rubygem is a package containing some code. https://en.wikipedia.org/wiki/RubyGems. Ruby on Rails is a programming framework, like .NET for instance. https://en.wikipedia.org/wiki/Ruby_on_Rails