Other than the default notification tones for text messages, you can use a MP3 file or any other audio files and set it as a message tone on Galaxy S5. Make sure you have stored the custom message tone in your phone, and do as follows to set it as text message tone on Galaxy S5:
See Also: How to Set Custom Ringtone on Galaxy S5
1. Open My Files application (The default file manager on Samsung devices)
2. Under Local Storage, open the Device Storage option
3. Browse the audio file, long press on it, tap the 3dot icon, and select the Copy option
4. under Device Storage, find the "Notifications" folder, open it, and Paste the copied audio file
5. Now, open the Messages application
6. Tap the 3dot icon and Settings after that
7. Tap the Notifications option, and then the Notification Sound.
8. On the opened list, you should now see the name of your audio file, and you just need to select it.