Hi, I am with you. I’m running the latest iOS version on my iPhone XS Max. Since a couple of months now iOS is not able to detect my language automatically. I am bilingual, English and German speaking and when using iMessages I was used to speak in any language and my iPhone was automatically detecting this language. I’m completely frustrated as I have the same issue in my latest iPad Pro. I assume it’s an issue with the Apple Servers but I’m not sure. The Apple Support so far couldn’t help me. The weirdest thing ever is that my wife is using an iPhone 8 and they’re auto detection of the languages is working fine. She can just start dictating in iMessage with any language either French or English and the dictation works just fine by automatically detecting the language she speaking.
feedback from Apple:
We currently don’t have an automatic language detection feature. When using dictation it will go by the last language used or selected. If this is a feature you would like to see, we recommend leaving feedback for us here: https://s.apple.com/dE4O8p1G1B
but this future existed in the past.