In addition to what others have already answered, consider that this is a responsive custom toolbar that lets you select from a huge number of languages, but it also detects languages being spoken. The control has to be flexible enough to allow for long and short language names without messing up the layout at whatever size the user views this interface at. Here's an example of what happens when you go one step deeper into the UI and start selecting different languages. A flyout menu opens below the little arrow. I said "Yesterday I ate a car" using the microphone and it detected English being spoken. Nicely done, Google.
Let's throw it a curve ball. I tested it by speaking into the microphone and it detected Lithuanian. It's got to dynamically indicate that new language choice right on the toolbar. That's asking an awful lot of a set of radio buttons. They are hard to maintain, so I can't imagine using them in this scenario.