Sorry to revive this old topic, but I think I found the same issue with Catalan (locales ca and ca-ES), at least in 8.1.37. While Spanish shows the comma as decimal separator, Catalan reverts back to dot like in English, but it should work the same as Spanish:
Is it the same issue as reported back then for other European languages, is it corrected after 8.1.37, or am I doing something wrong? Thanks!