The pPolyglots Polyglots

When you say "the polyglots," it sounds as if you're referring to a specific group of polyglots. Just "polyglots" is more general.

The polyglots... Hhow do they not forget so many languages? The polyglots...how do they not forget so many languages?

TheHow do polyglots... How do they not forget so manythe languages they've learned? How do polyglots not forget the languages they've learned?

Is it hard for them to use different languages regularly? Is it hard for them to use different languages regularly?

Your original sentence isn't wrong, but it makes more sense to add a word like "different". This shows that these people are speaking more than one language.

Is it hard for them to use so many different languages regularly? Is it hard for them to use so many different languages regularly?

If you think it's easy to practice one or two languages, I think it's easy enough. I think it's easy to practice one or two languages.

But if you learn five or more languages?... But if you learn five or more languages?...

You might want to add one more sentence at the end of this one, in order to clearly express what you're thinking. This is optional, and the sentence makes sense as it is! One note: in English, when we use multiple periods, we usually use them in groups of three, like "...". This punctuation is called an ellipsis if you didn't know

But if you learn five or more languages?. are a lot to juggle. But five or more languages are a lot to juggle.

I get what you're trying to say but it's an unfinished thought and feels awkward.