Thank you all! This is a great video! I wish I could just put subtitles on it, that would be easier.
Anyway the first part is relatively uneventful. It starts to get interesting when they're inside the clothes shop. Kelvin (the guy without a cap) hides in the changing room to hold himself secretly. Marvin find him of course.
Kelvin then tells him that he's slowly starting to feel like he can't stand it anymore and that there really is a lot of pressure on his bladder, which he feels with every step. Marvin then asks him, if they should go home but Kelvin refuses, because he wants to win. Marvin convinces him though and comments: "before you wet your pants"
Car Scene:
Marvin: Guys, this isn't funny anymore. I really have to piss now. I'm going to undo my belt, my little secret trick, because I have to win. I don't want to bite that potato. (the punishment for the loser is to eat a raw potato)
...they're on the road
Marvin: How are you feeling?
Kelvin: Very bad. How about you?
Marvin: Yeah, not too bad actually. I'm gonna win anyway.
Kelvin: I will still hang on, I'm not kidding.
Marvin: I think you will need to piss very soon.
Kelvin: You'll get the punishment.
Marvin: Look at all that water out there. Nature wants you to go to the bathroom.
Kelvin: Yes, I'd like that.
Marvin: *laughs at Kelvin while he's holding himself* Not funny anymore. Go right! No! Go right, dude!
Kelvin: No!
Marvin: Where do you want to go, dude? You have to go to the bathroom?
Kelvin: Don't talk to me!
Marvin: Hey, chill! Where do you want to go?
Kelvin: Shut up, now!
Marvin: Oh...he needs to go to the bathroom. Is it so bad, yet?
Kelvin: I definitely don't want to use my car as a toilet.
Marvin: It's already wet.
Kelvin: No it isn't.
Kelvin then convinces (or rather forces) Marvin to get out and go on a walk with him. Marvin fears, that he's going to run off and piss which he actually tries to do several times. Kelvin then makes fun of Marvin because of his belt and tells him that maybe, he should check his pants because they're black.
Marvin: Why do you want to go on a walk now? Are you serious?
Kelvin: I can't stand it in that car.
He runs off.
Marvin: Hey chill! Don't run. That will add more pressure. If you slip, I will laugh at you (funny thing is, that he's the one slipping at the end)
8:14
Marvin: Hey guys, I think I'm just gonna piss now. Or not? No, then I'll lose. I can't do that.
At 8:24 they're trying to convince each other to just give up and pee in the bushes.
8:47
Marvin: I need to piss as well.
Kelvin: *pretends to get a phone call*
Marvin: Guys, I think have to give up but I can't. It's getting really hard.
I don't think I have to explain the following

9:23
Kelvin: Guys, it's getting serious. I can't do it anymore.
Marvin: I couldn't do it before but I'm hanging on.
Kelvin: It's starting to get painful.
Marvin: Every step is torture, actually.
Kelvin: But we somehow have to make the other one pee. *starts holding himself*
Marvin: Already wet?
Kelvin: No.
Sorry guys, It's getting late. If you want more translations, just comment. I have to go to bed now lol.