Complex sentence: AES is the default option, and Twofish is available in 1.x, but will not be available in version 2.x-however a separate plugin provides Twofish as an encryption algorithm.
Split into simpler sentences: AES is the default option, and Twofish is available in 1.x, but is not available in version 2.x. However a separate plugin provides Twofish as an encryption algorithm.