Problems with voiceover pronunciation

Hi all,
I use iPhone 5s with the newest iOS installed and the Polish language set as default. I’ve noticed that VO has suddenly switched pronunciation of certain items e.g. app store, bluetooth, etc. It still speaks Polish but I can’t deal with this matter. I have set Polish as default and don’t know what else I can do. I’ve restored my device to factory settings but after some time the same has happened.
Please give me a hint what I can do.
Warm greetings and thanks in advance for your help.