There isn't any Telnet Cicode function or capability or feature of Citect SCADA that I am aware of. There is however extensibility via the .NET Cicode functions. Check out the online help topic:
https://www.citect.schneider-electric.com/webhelp/citect800/#../Subsystems/CicodeReferenceCitectHTML/Content/Net%20Functions.html
Then for .NET Telnet library, you could have a look at what people suggest on Stack Overflow:
https://stackoverflow.com/questions/390188/c-sharp-telnet-library