Around 1990 I attended ISO/JTC1 meetings generating standards for data communication. I still recall my surprise over the heated arguments over these words between the UK and the US delegations. (I'm from Denmark). In particular 'shall' and 'should' meant different things in English and American languages. ISO's first standard, ISO 1, states that ISO Standards shall be written in English so we had to do that, US delegation too. Similarly Scott Bradner stated in RFC 2219 how American conventions should be followed for future IETF STDs.

So I'm confident that the word 'shall' has a strong meaning in English; whether it has too in American legalese I cannot tell.