Download Mobile Speech Recognizer FREE Unity. 

This package lets you use speech-to-text OS engine.
On Apple devices it uses engine introduced in iOS10 – you still might target devices with iOS lower than 10 and use simple API to check if engine is supported.

Supports all major languages, such as English, German, Spanish, Dutch etc. – it detects language set in device’s settings and is use it in recognition process.

Extremely simple API:
onFinalResults.AddListener(…)
SpeechRecognizer.StartRecording();