Notarization of documents

Hey guys, long story short I'm currently assembling some documents in preparation to register for an international marriage with my fiancé. She is Japanese and living in Japan. I am British and living in the UK, the documents will be sent to her to handle with the city hall while I continue to live in the UK.
The plan after that is to work on a CoE (Certificate of Eligibility). But that is story for another day!

My affidavit is translated already and I will have it notarized in the UK. However, I am rather stuck with my birth certificate and passport.
They also must have copies translated into Japanese. I know a website that I can use to have these translated but it costs and awful lot of money if I want them to be notarized (about £315 each). I do not know if the translated copies of the passport and birth certificate even really need to be notarized, as they're just translations for the marriage registration. I believe they're for the benefit of the city hall workers which is completely understandable.
Regarding that, I have not been able to find any further information online.

I have read that most people in my situation just translate the birth certificate themselves, and that it doesn't need to be done by a profession or even be absolutely correct, just good enough to be understandable to the city office where it will be handed in. If so, then me and my fiancé could easily just make a word document and translate birth certificate ourselves. As for the passport translation, I'm thinking of having it translated but not notarized because the price is quite high and I'm not even sure if a notarization is necessary. With the notarization, the translation costs about £80. That's a huge difference from £315 just to have an apostille notarization. (I think in America it isn't called that).

I said long story short, but it seems as though I've rambled on quite a bit! I apologise.

tldr:
Do I need to notarize my passport translation and birth certificate translation for a marriage in Japan?
We are doing an international marriage so my translated documents will be sent by mail to my fiancé and she will handle it with her city hall while I am in the UK.

Short answer based on my knowledge of the process at city hall for registering a marriage, no.

Hi Goosie

It's me again who helped you before :)

As a British citizen who registered her marriage to a Japanese national in Japan, I will tell you my experience

The affidavit, it's my impression that this has to be notorised at the British Embassy in Tokyo. That was the case when I got married and I was told that directly by the embassy themselves. There may have been some changes due to pandemic so please email the British Embassy of Tokyo to double check the requirement for that if you haven't already

At the city hall, I didn't need a translation of my passport, however I did need one for my birth certificate. This didn't need to be an official translation or notorised. My husband just did a word doc and stamped his hanko on it.
However, every city hall has slightly different requirements and your fiance should contact them to find out what you need first

Hope this helps

@JapanCustomTours
@Shelly

Thank you both very much.

Shelly, I remember you! How has your job search been? I hope everything has been going well for you. It's nice to see your name pop up in one of my threads again hehe.
Regarding changes to the process, even I am not 100% certain of this, but I have read multiple threads on other websites of people essentially going through the same process as me and having it work. So I'm thinking that the process has indeed been changed slightly to work with the pandemic.
Thank you for sharing your experience with me! As I write this my fiancé is actually translating my birth certificate, so that's that sorted out. As for my passport, I think I'll try to do it without the translation and notorization at first and see what happens. It would be a nice little saving haha.

Again, thank you both for your helpful responses. In case any one finds them self in the same situation as I am currently, I'll try my best to post a detailed account of what happens when it does.

Just to add to the comment from @Shelly, the people I helped with the process only needed their affidavit notarized, and that was the "no impediment to marriage" document rather than things like FULL form birth certificate (watch that one, short form certs not acceptable) and other ID docs like passport. All of the other form filling and translations did not need to be "official". For the UK couple I was helping the office we were at had changed their process slightly so it took a bit longer even though we had all of the documents required, and the staff actually did some of the translation with us which was helpful of them.

@JapanCustomTours
Thank you for detailing the process for me. Yeah you're absolutely right, I need to be careful to use my full birth certificate, not a short form one. I'm pretty sure the one we're using is, it has both my parents' names, occupation, ect.
I'll go ahead and get the relevant documents translated and see how it goes. Like I said in the last message, I'll keep this thread updated on my situation as to hopefully help others.

Just for anybody in the future who is reading this and hoping to get some answers.

The documents were accepted by the city hall and the international marriage was possible. I only notarized my Affidavit, nothing else was notarized and it was absolutely fine.

If you are in the situation I was in, best of luck to you. I'm sure you'll be fine.