But adding a new language will just make it even more inefficent.
The idea being that eventually (though that would need to be far in the future) you would not need to translate as it is a common language among all member states.
Why not just use English which is already well established and even widley known amongst most European citizens.
Because it is a difficult language to master and it puts many non-native speakers at a disadvantage. As pointed out above, there are only two countries who do speak English natively now, but depending on your native language, some citizens still have an substantial easier time learning English.
There's a mismatch between the link and the title. Nothing about Paxster in the article.