Well, discuss mainly about English in your statement, and discuss your interest in languages as a whole, so mention Japanese as one of the languages you are deeply interested in and for reasons etc etc. Try to include the Japanese in, but bare in mind that 4 unis will see Japanese as an addition to your English skills, they don't only want to hear about the Japanese.
It's not impossible, but I think it'd be rather difficult to write a good personal statement that covers Japanese, History and English Lit.
You should really make your mind up because in your PS you have to convince them that you have an interest in the course and are fully committed to it...which would be hard to do if you do not have a PS that is not all about one course.
If you apply to less popular courses (the unis lowest in the rankings) then this might not be a problem but the better unis will receive lots of applications so they might not consider someone who's does not really show commitment to their course.
If you stick to one subject for all your choices then you can write your PS about that subject only which the unis will prefer.
I'm in the same boat, but not as complicated lol. I'm applying for English with either German or French at various places. I'm structuring like this
Para 1: ENGLISH and how great it is etc
Para 2: Languages - how great they are AND how they have complemented my English studies
Para 3: extra
Unless you include in your English paragraph how fascinating studying past literatures are and how key they are to unlocking past civilisations etc I don't really see a way of working History in there... sorry
sheffield uni does history and japanese, they also do linguistics and japanese which may be the right course for you
How are they hard to link? Ignore everyone that says it'll be difficult.
Focus on: Japanese history and culture, and why this makes you want to study the language.
How studying English Lit is really enjoyable, and you'd love to be able to study Japanese Lit (give some examples of what you've read in translation, perhaps) at some point in the original language.
And History and English Lit is easy...They're both quite similar in the way of thinking needed to approach it. So just go on about what periods of history you like, what you've read that reflects this, what you like about the literature from this period (and in general), how you love interpreting things, writing essays, etc.
Don't lie, though...