Hello! thanks for your comments! Speaking with Georg, he suggested to simply add a negative kern between space and guillemetleft and so on in French only (using language FRA into a kern feature). It would be easier than a ligature. And yes, if an user uses the correct space (thin space) no substitution and no kerning happens.
In the European Author Rights law there is a concept called “anteriority”. If an Author can prove and document she/he gave a certain name first to a font, he can claim legal protection against you in his country. What said apply to individual artists/authors, not to companies who should register their names.