This page is just a reference of all the known Steam APIs, I do not know how they work. Please do not email me with questions.
PUBLISHERPOSTSetRichPresenceLocalization

Save and commit rich presence localization for the given app

https://partner.steam-api.com/IProductInfoService/SetRichPresenceLocalization/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 Yes
{message} Yes
uint64 Yes