Pronunciation research for app Hello does any one know or at least can lead me to the right way?

What does not change pronunciation of words when someone is speaking. The idea is to create a app that checks if word/sentence is pronounced correctly. To do so I need something in pronunciation that does not change at all or changes in small range.

For example someone reads a text. His voice is recorded. Now someone else, who can not read so well reads it too. Then the recordings are compared to eacother. Then software displays on the computer screen how wrongly the second person pronounced.

Please do not suggest any software that does it!
You need the right audio features, and the modern way to do this is with deep neural networks, which learn them automatically. I would use one built for speech recognition (it's basically the same problem), then model the users by the output of the top layers. Accents should manifest as clusters of the features, and languages as superclusters. I don't have much experience here but I'm making an educated guess.

Here is a relevant paper (Deep Neural Networks for Acoustic Modeling in Speech Recognition), and here is a relevant student project (Accent Recognition with Neural Network).