Other than US FDA definition, are there other standards for vanilla extracts?
There's not really a European equivalent for the FDA's definition of extract (by ethanol percentage). Instead, the EU specifies what constitutes natural vs 'vanilla flavouring' (euphemism for 'artificial').

See the EU's white paper on it here (notably page 15): 
AUTHENTICITY OF VANILLA AND VANILLA EXTRACTS

Also, in plainer speak, info on vanilla industry standards between the US and EU here.

Additional reading: the EU directive ISO 9235 specifies what can be listed as artificial/natural and covers vanilla/vanillin.