They are disjoint sentences. “... beasts can understand your speech, and you gain the ability to decipher their noises and motions.” You have this ability.

You can always understand beasts. Your ability to make them understand you is limited by your current form’s speech ability. The definitions of [speech][1] all indicate that it is through sound but some further limit this to words. Your agape form can make sounds but not words, your fish form can do neither - you need to ask your DM..


  [1]: https://www.google.com.au/search?q=speech%20definition&ie=UTF-8&oe=UTF-8&hl=en-au&client=safari