a level choices

The subjects you have picked out sound great! A science background can help you in lots of different ways later on, and having a language and a social science are great options if you wanted to do modern languages/international relations.
'Variation' isn't a necessity, your best choice for A Levels is ultimately what you think you will enjoy, and what you need for what you want to do after A Levels are over. So if you are quite set on a particular course at uni, focus your choices around what will help you in that subject! If you are less sure, having a variety of subjects can be great to keep your options open. For international relations, having essay-based subjects and in particular social sciences will be really beneficial, and for modern languages, once again essay-based subjects and really as much linguistic/language experience as you can get. Some other subjects you might be interested in in the general IR field are:

I'm really interested in studying languages and am considering studying modern languages or international relations at uni, but I'm struggling with A-level options.
I have chosen politics, Spanish and chemistry, but it isn't too late to change them. i know i want to study politics and Spanish, but am super unsure on chem. I wanted to study German but am not able too due to scheduling since it would involve me attending three separate schools, which is of course not allowed. i was a bit pressured into choosing chem by my family because they said that it would show variation when applying for uni. I am predicted 9-9 in double science so it isn't really a case of not being able to take it but a case of whether it is really worth it. I'm aware that chem is considered a very hard a level and i spoke to a friend of mine who did it and studied english at uni and she slightly warned me against it if i don't plan on pursuing it.
So, I was considering taking economics instead, a subject that i have never studied but sounds like it could potentially be a bit more related to my subjects than chem.
Please help me on this i honestly have no clue and it's stressing me out a bit.

Spanish and Politics are excellent choices for you given you are aiming for an IR or languages based degree in the future.
For your third subject you should be looking at options which you will not only enjoy but also be able to excel in without it putting strain on your performance in Politics and Spanish if your third subject is not as relevant to your degree ideas (eg: chem). Im not suggesting at all to not put effort into your third just that if it’s less relevant you should focus your energies on achieving your absolute best in Spanish and Politics.
For a languages based degrees preferred subjects are language and English although there are typically no specific subject entry requirements. For this as you plan to take Spanish you should be fine but if you’re looking for options which will be relevant to your options then you might want to consider English.
For an IR based degree there are again no strict specific entry requirements but Politics is an excellent choice. Other relevant ideas include: history, geography, law, English, sociology, economics. History is often one of the most common a levels held by applicants, not saying its an advantage but may align well with the interests of those who are also interested in international relations.
Basically you can choose anything as long as you are confident you’ll enjoy and excel at it. Happy to try and answer any further questions you may have and I hope this was helpful. Have a lovely day

Spanish and Politics are excellent choices for you given you are aiming for an IR or languages based degree in the future.
For your third subject you should be looking at options which you will not only enjoy but also be able to excel in without it putting strain on your performance in Politics and Spanish if your third subject is not as relevant to your degree ideas (eg: chem). Im not suggesting at all to not put effort into your third just that if it’s less relevant you should focus your energies on achieving your absolute best in Spanish and Politics.
For a languages based degrees preferred subjects are language and English although there are typically no specific subject entry requirements. For this as you plan to take Spanish you should be fine but if you’re looking for options which will be relevant to your options then you might want to consider English.
For an IR based degree there are again no strict specific entry requirements but Politics is an excellent choice. Other relevant ideas include: history, geography, law, English, sociology, economics. History is often one of the most common a levels held by applicants, not saying its an advantage but may align well with the interests of those who are also interested in international relations.
Basically you can choose anything as long as you are confident you’ll enjoy and excel at it. Happy to try and answer any further questions you may have and I hope this was helpful. Have a lovely day

but just wondering, if i were to apply to study mandarin, would i be able to study it without taking english, even though i have never studied mandarin before?

Im assuming you’re talking about studying mandarin at degree level here, if not then let me know what you meant and I’ll look into it.
There are actually only a few uk undergrad degrees which are all something with mandarin (like history, business, English or education) so its limited and has to be studied in a degree alongside another subject from what I can see. You can also study mandarin with education to become a teacher ig so that’s an option if that’s something that interests you. The degrees I’ve looked at which are something ‘with mandarin’ and mostly seem to not have entry requirements, there’s occasionally like something about having studied any language before but it doesn’t have to be mandarin.
You could instead opt for the route of taking Chinese studies or studying modern languages (specialising in mandarin) which is perhaps more what you wanted than studying another subject with some mandarin. Some of these require a grade in the language you wish to study so Mandarin but others say they can be studied at entry level and beginner so no prior experience with the language is required. Therefore you can study mandarin this way without taking it for a level.
Hope this helps you out, have a great day!