We have recently started playing DnD 5e with a group of real life friends. I have many years of experience with various PnP games under my belt and have also played DnD for a good amount of time and would call myself experienced.
My friends on the opposite have never played any PnP games. They are enthusiastic and willing to learn and creating our characters already went quite well - everyone got a character they are very happy with and understands their strengths and weaknesses.
The first campaign we played was led by me, it was a short, simple introductory adventure I made myself and was mostly built to show them the game mechanics by more than subtly hinting towards what they could potentially do in a situation (being on the look out for traps while in a cave system or maybe checking if the intentions of their opposite are what they seem to be, stuff like this). I think they got a good grasp of the game and when we ended the campaign at level 3 they were looking forward to playing another one.
For this second campaign one of the players now asked me whether they could lead it this time around. I would join the group with a fresh level 3 character. I agreed to this as I personally prefer playing over DMing. However, them being new they aren't too sure about most mechanics, how to balance out encounters in a decent fashion and so on. They created their own story, set in resemblancy of a fantasy universe they really enjoy, but in many occasions started asking me how to overcome some obstacles they are facing. Those are often related to language barrier problems as English is not their native language and it is sometimes hard for them to follow the English material and guides.
I have helped whereever I could, but it becomes increasingly hard to do so without getting to know the whole story beforehand.
So, with all of that backstory (sorry for the chunk of text) let me come to my questions:
How can I help our new DM to lead the campaign to be successful without getting to know all of it before we even started?
How can we all enjoy the campaign without me leading the group by pointing out mechanics/ideas all the time (which gets obnoxious I fear) that they might not have considered yet?
Thank you for all your input, wanted to give a quick update: I talked to them regarding NathanS' answer regarding Co-DMing and they reacted really positive. We talked about the whole first chapter of their campaign and already found some issues and places where the PCs will probably not do what the DM intended. It was definitely a good idea to do this, I am now really looking forward to the campaign and how the others are going to play along (or not).
HellSaint's answer to give them DM tools is also definitely something I will keep in consideration for the future. I already translated some of my spreadsheets and will do so for some more and give them to them to work with. I will definitely try to provide them with tools in our native language so that the language barrier towards English is as minimal as possible. I started translating all spells and mechanics for that reason, too so that they have resources they can build upon.
Thank you all again for your input! I am now looking forward to a successfull campaign.