As you said, each leading on all passports has equivalent (even on one of the page you've got the numbers referred in different languages for EU passports). When you travel abroad (within the EU - for other countries you may need a visa and therefore checks are done before), customs in airports do not need translations to check passports, and in addition, with nowadays passports they can also check the validity electronically. Therefore I don't see the need for a translation, especially within EU.

However for some other countries (Arabic, Chinese) there might be a need.