My INDEX field already use the \z switch with language code 1036 (i.e. French), that's why it is mysterious to me. I couldn't see any difference in my index with or without the language switch, but it is probably unnoticeable.

Here is what my index field currently looks like :
{INDEX \r \z "1036"}

Maybe I can replace the ": " manually thanks to fields, just like the \d \e \g \k or \l switches, but I couldn't find one for subentries.

Apart from my language, how does an English-speaking user do to change the default ": " mark if it is not to their liking?