Telegram messages and HTML emails support Unicode characters (these are characters that are not covered in the ASCII set of characters. Emojis are very frequent representatives for example.). So if you want to use Unicode characters, you can easily do that by using Unicode code points in your text in the MQL code.
// A single or double escaped Unicode code point in this text string textToSend = "Some text with emojis -> \U+1F601 \\U+1F601"; // will produce "Some text with emojis -> 😁😁"
If you use only one backslash the MQL compiler will warn you (see the error pane in the MetaEditor) about the unrecognized escape sequence. You can avoid that by using the double backslash.