Splashtop On-Prem for Android supports two input mode: Key Mode and Text Mode. You can change the input mode by tapping the gear icon when in a remote session.
Key Mode
In key mode, every character input on the keyboard will be sent to remote side directly.
Text Mode
If you would like to send a local suggested word when inputting text, you can change it to text mode, it will show local suggested words, press the suggested word to send it to remote computer.