There might be many reasons:

First, Senketsu was created specially for Ryuuko. This might have created link, that allows them to understand each other. It is clear that Senketsu doesn't really "talk" using his mouth. It is more like telepathy. This telepathic link might have been created either intentionally or accidentaly when Senketsu was made.

Second, there is question of relationships. Ryuuko and Senketsu are partners or friends. For them, it is symbiotic relationship. Satsuki on the other hand uses her willpower to dominate Junketsu so it can be used as a tool. And as such, there was no reason for her to listen to it, so even if Junketsu did talk, Satsuki would simply make it shut up, because Junketsu talking isn't what she need. Ryuuko and Senketsu were partners so it was obvious they would talk to each other.

And last is simply about production: The creators simply didn't think of Junketsu as character. And as such, they didn't give it any voice. Senketsu was individual character from early start and as such it made sense to make him talk. And as such, he helped character development of Ryuuko. Junketsu on the other side was just something used by Satsuki.

Why is Senketsu the only Kamui that can talk?
I have Android 4.4.3 on a Nexus 5.
I connected the phone to a laptop, and there I deleted most of the files in the Downloads directory of the phone.
Nevertheless, these files still show up on the phone when I open Downloads (of course, when I try to open them, I get an error).  

Is there a way to refresh the Downloads list?
