In the fifth part the same variant of the cipher already introduced in Part 3 and 4 of this challenge has been used here, too. The only difference is that spaces were removed previously to the encryption process.
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The only difference is that spaces were removed previously to the encryption process.

Hello.
Does it mean that the plaintext is in English in Part5, too?
Or may be the language of the plaintext is to be discovered during solution. Is it?
Thank you.
Dusan

Does it mean that the plaintext is in English in Part5, too?

Yes, it is in English.