If you use a new iPhone with iOS 11, and you send text using the Indian language Telugu, the character will crash your messaging app.
Not only that, it can also crash WhatsApp, Outlook, Facebook Messenger and Gmail. These apps can be disabled once a message with Telugu is received.
Skype and Telgram seem to be unaffected.
The only workaround is to ask the friend to send a message and try to delete the conversation thread which caused the crash.
Apple should have a fix out soon.
There's more info here on the The Verge website