TLDR because of racism.

For what its worth, I found drawing / sketching while we talked to be helpful when trying to exchange ideas with students from China while in studio in the US. It seemed to work out ok when I was doing group projects in Hong Kong / Japan too.

Personal opinion, group projects suck though.

It seems like an extreme case in your studio. If all but one is from the Mainland, then they're practically back in China as far as the studio environment goes. I can definitely see you being the outsider, even if they didn't go out of their way to ostracize you. Similar case with Koreans - probably the second largest group of international students from my experience - who are also quite cliquish. Students who do not find themselves surrounded by their countrymen tend to interact more with other students, if only because they have to.

How's the quality of their work? Do they know their **** or are they mostly second-generation wealthy kids dicking around in the UK? Most Mainland students I've encountered are dead serious about their work, smart, hardworking, and will not let a lack of a common tongue stand in the way of collaborative work. They're here to learn. Sure, they might mostly hang out with their countrymen outside the studio but it's all business inside. From your description, it seems like the cohort in your studio is plain uninterested in their work - or at least group work, which is always terrible LMAO.

Communicating via visuals should help for a start - sketch out ideas, model some rough stuff. Short of informing your instructor, being blunt might be frowned upon to some but I think if you're being respectful and result-focused, laying out the communication problem to them in plain language could help. Unless they really don't GAF about their grades and just want a shiny British degree to take home.

Learn Mandarin? 

1. try making friends with individuals instead regarding them as a singular group. it's unlikely they all know each other or share a common idea for doing the work. find your one or two friends in the group and keep focused working well with them only.

2. don't be the spokesman for the instructor. this isn't your job and letting the tutor regard you this way will make your life miserable. if he can't communicate with the class, that's his problem. really important, don't let the tutor delegate this to you, or you'll be seen as responsible for coordinating the work of the group. which you can't do.

3. group projects for university students are idiotic and always lead to poor results, regardless of the quality of students in the group. groups need leaders and hierarchy, and a team sharing a vision; a studio provides none. don't even try to make it work, just choose your piece and do it as you want to.

any tutor who assigns a group project is fully responsible for coordinating the tasks and making sure everything comes together smoothly. they won't do this though and nothing will come together. this is why there are no good group projects in school.

I worked in Japan for a bit. Japan and China are very different culturally, but generally East Asian culture is passive when it comes to communication. They rarely take credit for their own work, they are slow to accept praise or compliments, and ironically in your case, they believe in a collective pursuit. 

With that being said, although their English may not be the best, I can guarantee you that the receptive English language is very strong and they probably understand everything that you're talking about. Also, you're lucky enough to be in a profession that's a universal language. You communicate through drawing and sketching, showing precedents and diagrams. Find a commonality and use that as a means of communication. 

A lot of students in architecture school hate working in groups because they're not used to sharing ideas and delegating work in a group setting. The majority of the time they have been cooped up in their own little design world. Group projects are actually a great time to learn how to delegate work so that you're not overworking yourself, sharing ideas, and collaborating like you do in the real world. 

Finally, you are all grown ups. Architecture is a very international profession and you will meet people from all over the world. Common ground needs to be found. If you feel they are not fairly contributing or they are putting explicit roadblocks in collaboration, then let your teammates know that. I guarantee you they will understand what you're talking about once you start talking about grades and getting instructors or administration involved. Talk to your instructor or the head of the program if things escalate. You are paying for this education.

I cant say for sure but I figured that yes means yes and 'yes,yes' means no and/or not sure (without admitting that they didn't understand). Group work sucks...also find a better studio or class for next semester. That school is just lining its pockets with higher fees if there are no locals...

Also sketch more, then its on paper as a draft - outlined.

Most of my co-workers for the last 7 years are Asian. I've found the best wat to communicate is via sketching, Bluebeam. Revit, Rhino, sketchup. anything visual

As a Chinese native, I would say this is most likely because of the language barrier. Many Chinese students you see in a UK master's program are not capable of communicating in English in real life. I have to admit that most of my countrymen speak poor English that sometimes even I can't understand them. Your teammates make you the spokesperson by default because they are aware that they can't speak as well as you do. They feel grateful that you speak for them (maybe they won't tell you but trust me, they do).

It seems, in your case, they are very reluctant to talk to you. This could happen because some of them would rather have you being a free rider or a mascot than having to communicate with you. If you want to free ride, do it, they won't be mad at you. If you don't, be efficient and try to split the work into parts and assign them to each person. If they keep quiet, it means they don't disagree with you so you can do whatever you want.