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.
PUBLISHERGETFilterStrings

Filter a list of strings in the requested language with rules that match the client.

https://partner.steam-api.com/IContentFilteringService/FilterStrings/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
int32 Yes AppID that is asking to having filtering performed.
string Yes In which language should filtering be performed. If empty, no profanity filtering will be performed.
string Yes If set to an ISO 3166-1 Alpha-2 country code that requires legal filtering, that legal filtering will be performed.
string Yes The list of strings to be filtered.
bool Yes True if the strings are names instead of chat text
uint64 Yes The SteamID of the person viewing the text