Neither of these is *very* strong for retail, and neither RSM nor EMLyon is very well known outside Europe. In the retail industry, the language issue isn't more or less profound in France than in The Netherlands.
The top schools for retail in Europe are IE, Insead, IESE, ESADE, LBS, Henley, Cambridge and HEC. One advantage that EM Lyon has is a modest relationship with Carrefour, which is a hugh retailer. RSM has fewer people in the retail sector than EM Lyon, but it is a bigger brand and perhaps a better MBA.
I applied to both RSM and to EM Lyon, and was accepted for both, so I am balanced between them.
RSM is certainly a more famous school. For retail and for entrepreneurship, EM Lyon is perhaps stronger - but not by an order of magnitude.
EM Lyon, of course, is cheaper. France has the CAF scheme, which means rent will be heavily subsidised. Lyon is also 19% cheaper to live in than Rotterdam (http://www.expatistan.com/cost-of-living/comparison/rotterdam/lyon).
What do you think?