I've had a stutter for many years now which makes speaking difficult at the best of times. Combined with the pressure of 5 minutes being worth 25% of your entire language exam grade and having to memorise endless flashcards of questions, oral exams and I have never gotten along well. But I've learned some tips over the years and I hope the knowledge I have to share can help someone else.
Figure out your weaknesses in speaking
Don't just say 'everything. I cannot communicate and I don't want to open my mouth ever again' (although, what a mood). Stutters are generally worse in stressful situations, but what sounds specifically? Vowels? L's? M's? Is starting sentences more difficult?
If you're in a stressful situation (for example, talking to a teacher or telling a friend something important), reflect afterwards on what sounds were difficult for you to say. Recordings are also a good way to put yourself under pressure and figure out what sounds are difficult for you to make under stress.
Your brain is a computer, find the bugs and work around them
So M's are difficult for you to say? In what situations? Start of words? Start of sentences? Middle of sentences? For example, M's are difficult for me to say if they're at the start of a word, but not if they're in the middle of the sentence. So if possible, I try to avoid putting words beginning with M at the start of sentences.
Ex. Ma maison est assez grande.
This is difficult for me to say.
Ex. J'habite dans une assez grande maison.
This is far easier for me to say as the M isn't at the start of the sentence. Find these loopholes and exploit them mercilessly. Use synonyms so you can use a different word than the one that gives you difficulty. It'll also increase your marks for varied vocabulary!
Make your oral flashcards well in advance and start memorising them as soon as possible. Memorised lines are much easier to say for me, so this is something I find very helpful. Look at them whenever you have a spare moment - waiting for the teacher to hand something out, on the bus, in the dinner line when you're not involved in the conversation at that particular time - and memorising will be a lot easier.
Ask for extra time in the exam
There's no shame in asking for extra time, it's what you're entitled to. 20% extra time is the norm for the CCEA exam board, but the actual amount of extra time may vary. 20% may not seem like a lot, especially for shorter exams, but those extra seconds will give you time to get your words out, especially for the dreaded first question of 'what's your name?'. You will have the time to get onto the longer questions and really show off what you know!
'Normal conversation rules' don't apply
You don't have to make eye contact with the examiner - you can stare at a wall, at the floor, at the desk grafitti, and the examiner won't care - they're too busy making notes anyway. As long as you speak loudly enough for them to hear you, you don't need to look at them. Personally, I hate eye contact, so not having to make it takes some pressure off in the moment.
I was also allowed to take a fidget item into my (mock) exam to help me manage my stress, and the combination of not having to make eye contact, doing the Leg Bounce™ and being allowed to use my fidget item helped reduce some of the stress I felt. You may have to ask to take a fidget item into a real exam, but there shouldn't be any reason why it's not allowed as long as it isn't particularly noisy.
Remember: you've got this. Stutters are incredibly annoying and cause a lot of stress, but there are methods that you can personally use and accommodations you can ask for to reduce the burden on you.