Do other players hear Krieg's inner voice?
According to A Meat Bicycle Built for Two film, Krieg's sane self can only talk to the psycho and urge him to say things "outside".
Can rare phrases of sane Krieg in-game be heard by other players?
Yes, they can (tested playing with zer0, Maya, and Salvador.) However, it's usually so quiet that other players can't hear it unless little else is happening and music volume is turned way down.
Yes
There are many sentences that we hear coming from the inner voice
Krieg seems to suffer from Multiple Personality Disorder (MPD). He argues with himself in some of his quotes, and he has a very quiet 'inner voice' which occasionally tells him what to do or comments on his surroundings--it is very difficult to hear unless sound effects and volume are turned down very low.
In the Krieg page on borderlands wikia you can read all his quotes including the "inner voice" quotes.
Quotes of the "inner voice"
Parentheses indicate Krieg's psycho voice speaking.
When joining a game
- If I harm an innocent person, kill me.
When using Buzz Axe Rampage
- This is gonna get ugly...
- You asked for it...I can't hold it back any longer...!
- It's time...
- No, don't do it!
Silence the Voices (Self Damage)
- Dude, what are you doing?
- I deserve this.
- You can't get rid of me THAT easily...
When reviving an ally
- That's right, help 'em. Just like old times...
When revived
- Say 'thank you'.( NIPPLE SALADS!! )...Close enough.
On earning a Second Wind
- Get up...you still got bad guys to kill...
- On your feet, she might still be out there.
While Idle
- Where is she? Is she still alive? Did she get away?
- If you ever kill an innocent person, I will destroy us.( Shut UP!! )No. That's the deal. You can kill as many of the deserving as you like, but the second your axe touches the flesh of an innocent, I'll end this. All of it. A razor to the veins, just like that fugitive we tried to grab on Hera, remember?( Nnnnngh, get out of my head!! )
- ...I'll take that as a 'yes.'
- Nice change of pace not to be murdering someone for once. Probably temporary, though. I'll lose my mind again and be screaming about meat and fluid soon enough... But this part feels... nice.
- I'm beginning to remember( Stop it, keep the memories down with a knife in it's throat, slash it until it bleeds thought juice across the dirt and it's absorbed into nothingness...)
- I can't stop, I can't stop the killing( AND I DON'T WANT TO! )
Completing a Challenge
- Maybe the world is sending me a sign.
Comparing Items
- Uh-oh. Math. Hope we don't pop a blood vessel.
Spotting a Badass
- This one, we can kill.
When set on fire
- I deserve to burn...
- Ow. Ow. Ow ow.
When killing Hyperion troops or loaders
- Yes, make them pay for what they did to us...
When hit by friendly fire
- Oh...they finally turned on me...
When turning into a Badass Psycho Mutant
- I'm a monster...!
- You wanted 'im? You GOT 'IM!
When using Redeem the Soul
- Better this way...
- You don't deserve this. I deserve this.
When finding rare loot
- We can use that to kill the deserving, grab it..
On gaining a level
- Nearly as good as getting paid
When gaining Elemental Elation stacks
- (Stack the frenzy!) Say this with two different styles, the other with a calm voice and the other with a more angry tone with the added words: "Do it!" after
When accumulating Bloodlust stacks
- This is kinda awful, but mostly awesome...
Issuing a duel challenge
- Don't kill this one, they are not deserving.
Receiving a duel challenge
- Don't kill them, this is just for fun, for fun...
Winning a duel
- Teasingly (You should've ruuuun!)