If we want to use only one official working language, it should be Esperanto. This would be neutral for any country (including Ireland and Malta). This would not be a threat to other languages and cultures. Esperanto is easier to learn than any naturally evolved language. Its benefits are clear, it only needs a political support to thrive.
Let's get your facts straight: > Esperanto is easier to learn than any naturally evolved language. ...only for many Indo-European speakers.
There are probably many cases where it would be easier for a native of some language to learn a specific similar language (i.e. for a Dutch speaker to learn German, or a Portuguese speaker to learn Spanish), but I would not be surprised if Esperanto minimizes the cost function for the net effort required for all native speakers/all second languages.