the button is the least of your worries, and having decided to use an if/else or switch gets you about 1% of the way to where you want to go.
the more important question would be where does the translated content come from? Do you have three separate files, with the content of the page in their respective languages? Or do you use some other automatic translation service (like google, but I guess different? And while we're on that, what is it that you want that the google widgets do not provide?)
I wouldn't put a whole lot of faith in the language packs, either, btw - if you change the language on moodle's home page you will see that only little snippets of unimportant text get translated.