This is very, very easy. Google "cyrillic keyboard" or just install the Cyrillic keyboard support on your phone. Many letters in the Cyrillic alphabet look exactly like their Roman counterparts, but are completely different sounds and meanings. Cut and paste the Unicode into the chat, in place of regular letters. For example, 'Неllо' looks exactly like 'Hello' in most fonts, but is actually 'Nello.' I know you doubt, so check it out in a Unicode inspector: https://apps.timwhitlock.info/unicode/inspect?s=%D0%9D%D0%B5ll%D0%BE
The reverse also works. E.g., TPAKTOP B CPAKY means 'tractor into ass', and I typed that using 100% Roman characters.