This extension will hide text prompts in Duolingo, allowing you to focus on the audio. You have the option to type what you hear in a text box. It can inform you if you're correct but it only works with sentences with simple accents like french and Spanish, probably not Russian and alike.
You also have two audios from google Translate, one a slow version, giving you a total of three audio versions.
If you really want to focus on your listening skill, just translate without typing what you hear and accept errors when you mishear a sentence. That way you get do that sentence again and train your ears.
It's in no way perfect, but if you want to focus on audio. It's useful enough.
My advice is to finish the tree first, then reset it and use this extension to focus on audio. Otherwise, it would be too frustrated learning new words with audios only.