As far as I know INaturalist does not know how to capitilize common names, so the best way to handle this is to add them capitilized.
https://www.inaturalist.org/taxa/49321-Mesembryanthemum and use Dutch
Somewhere there is a discussion about Capitals and Common names, probably github.
https://forum.inaturalist.org/t/species-naming-conventions-and-capitalization-in-non-english-languages/8730