In any language, with time, the pronunciation differences occur automatically. Different people have the tendency to pronounce some letters, words, phrases etc. in their own distinct manner, often completing confusing the real pronunciation.
Sanskrit is a no exception in this; however, due to the strict sound-based philosophy, it has preserved its rules intact.
In India, there are some pronunciation differences when it comes to people coming from North and South.
The vowel ऋ represented phonetically as Ṛ is one such example. This photo will give you the real-life example as to how its pronunciation differs across Indian geography.
In North India, people tend to associate it with the English representation of ‘ri’, while in South India, it is represented in English as ‘ru’.
According to the deeper philosophy of Sanskrit alphabet, particularly stressed in Kashmiri Shaivism, Ṛ is the Amrita bija mantra.
Its pronunciation is from the retroflex position where the tongue is curled back a bit.
In reality, there is no association needed of ‘i’ or ‘u’. Vowels themselves are sounds and does not need any extra sound.
The picture that I have provided in this article explains it pretty nicely.
Similarly, there is another word that has this pronunciation confusion. Rishi in North India and Rushi in South India, while it is Ṛṣi in Sanskrit.
I hope this clarifies the confusion a bit. The correct pronunciation of all the Sanskrit letters of course comes from practice and practice only.