As per the subject, in the UK this happens so I cannot use the word "period' as an alternative. This is a variation on a long-standing issues still not resolved but introduced for me with IOS 14:
...When using dictation in any application, and this is very random, when I say the words ‘full stop’ so that it adds a . to the end of my text it will randomly also add the word paragraph with a capital P. So it looks like this
. Paragraph
I have deleted the custom dictionaries and words et cetera and this lasts for a short while but it’s come back again. I have now done a full reset and set up as new on my phone and the problem still exists.