If I remember correctly, the English ‘thou’ used to be the informal/singular as opposed to formal ‘you’. Also that a lot of Indo-European languages informal pronoun starts with t- because of the same root word: ‘thou’, ‘tu’, the Russian version (I don’t have a Cyrillic keyboard on my phone but it sounds a little like ‘tuh-ee’.

I’m sure a linguist on here can correct me on this if necessary!