Key information can be lost in translation
Different conceptual systems have different conceptual organisations, and those differences are cognitively significant. If the different organsations are translated into a universal conceptual framework, significant differences are eliminated.
Some conceptual organisations can't be translated inot a universal conceptual framework. Humans can shift between frameworks without eliminating the differences that are lost in translation.
Notes: Lakoff cites Mixtec (a native Mexican language), as well as the work of Benjamin Whorf (1956) in making this argument.