Hi!
Mobile Issues
I have checked the menu source under mobile inspection panel. It appears, that the mobile script moves the plugin output from a menu element to a link data-title attribute for some reason. That is unfortunately a menu issue, as the plugin has not effect on this behaviour. I guess it is to do some sort of animation/compatibility trickery within the menu script, but it’s a very bad practice to move DOM nodes from one place to another, as it not only creates parsing issues, but the registered event handlers are de-registered – meaning that placing any interactive element to the menu will most likely be broken.
I suggest checking the menu configuration, maybe there is an option to stop this behavior, so it simply prints out the plugin output, without moving it to attributes, or altering it in any way.
Translation Issues
I checked the WPML translations list, but the placeholder text seems to be untranslated there, for search instance 3 and instance 1. Search no. 2 is translated, and it shows the italian for me on the front-end.