Android: Speech Recognition without using google server
We used to recommend pocketsphinx, but now more advanced technology based on Kaldi toolkit is available.
The demo is here: Vosk API, you can simply load it in Android Studio and run. Full disclosure: I am the primary author of Vosk.
It supports speech recognition in 7 major languages - English, Chinese, Spanish, Portuguese, German, French and Russian.
If the speech recognizer has limited vocabulary (as in a simple voice user interface) and is limited few samples - it maybe possible. Applications such as Transcription is not a likely task to be performed on Android (in offline mode). Also DSP is required for Voice Recognition ... A limited vocabulary and limited to very few samples might be your best bet.
If you really want to invest time and manpower for your goal, look at the Java-Project Java Speech API 2.0 (JSR 113).
It is used on "normal" mobile phones for voice commands and works offline.Unfortunately, the project is discontinued.