The difficulty of translation

A catchy tune, created by a Belgian composer, has been translated in 100 languages (at least). Yet many translations miss the most important lines of the original:

L'égalité veut d'autres lois
Pas de droits sans devoirs dit-elle
Egaux, pas de devoirs sans droits.

Freely translated "Equality demands different laws: no rights without duties, no duties without rights". But in translations, the duties seem to go missing. Strange...