Switching voice or accent during Speak Screen when reading same language

I hope to switch the voice on different languages via Speak Screen. It switches voice and accent on different sentences or paragraphs even when all the text is in the same language, in my case English. - Nothing to do with any translation being needed. - This happens on web pages and pdfs and not just on word processor documents where there might be a language field embedded. - I've got an English UK voice installed and reading an English document it keeps switching to a Spanish sounding voice speaking in English that is very difficult to understand and yet there is no Spanish sounding voice installed on the phone. Using iOS 14.4 so everything is up to date. Please help with my project