When using the deprecated SMS/Messages resource URI to send text messages, messages with one or more non-GSM characters are limited to 70 characters. Any SMS messages that include 1 or more non-GSM characters will be separated by Twilio into messages of 70 characters or less on the recipient's device. However, Twilio will not create separate messages with unique message SIDs in your Twilio SMS logs. In your Twilio SMS logs you will still see the message as one message SID.
You can find out what characters are included in the GSM set here. You can also paste the text you're attempting to send into our Message Segment Calculator to verify your messages are free of non-GSM characters.
If you are sending unicode messages to mobile numbers in US and Canada, try the Messages Resource URI instead. With this updated URI, you can send messages containing up to 1,600 characters without being split on the recipient device. However, please also note that behind the scenes, SMS carriers still handle messages in "segments" regardless of the URI used, and SMS are billed per segment (This does not apply to MMS). The recipient should still see these as a single concatenated message using the new URI."
Check out the FAQ Does Twilio support concatenated SMS messages or messages over 160 characters? to learn more.