I upgraded the plugin to version 2.5.21 but there is a problem in the html code.
Before upgrading (2.5.20):
<ul class="qtrans_language_chooser" id="qtranslate-chooser"><li class="active">
After the upgrade:
<ul class="qtrans_language_chooser" id="qtranslate-chooser"><li class=lang-it active>
The "" after the class are missing.