Problem solved. Just found the possibility in the Speed Booster pack to exclude some files from being deferred.
I just added jquery.js, flags.js, toolbar.js and load-toolbar.js to the exclude list.
Now everything is working just as it should.
Just a quick update.
I’ve found the reason why it’s not working.
I’m loading the js files of my wp installation in the footer and with the defer attribute, using the Speed Booster Pack for WordPress.
(See here Speed Booster Pack)
Seems that google translate isn’t compatible with the deferred loading respectively loading in the footer. Anybody here who has an idea how to solve this problem?