There are various examples of criminal norms in European instruments that are potentially vague.
Examples include the European instruments on terrorism, child pornography, racism and xenophobia.
The core criticism of vague European definitions of crimes is that they prevent the national legislator from respecting the lex certa principle.
An additional example relates to the definitions of the elements of the general part of criminal law. Framework Decisions and Directives include the obligation to criminalise certain forms of participation, negligence and attempt without providing a definition of those terms. Thus, the Commission in its Annex to the report on the implementation of the Framework Decision on terrorism refers to the problems created by the different interpretations of the term ‘incitement’ in Italy, Spain, France and UK.
(The Principle of Legality in European criminal law, ed. Intersentia, decembrie 2015, la p.pp. 200-2)