Im learning chinese right now, dont know enough to write down my dreams or I would. 
i am learning japanese, though for other reasons than dream jounals. i find the idea so constraining, as i never have time in the morning for such things, but i do see the point…
there are an almost infinite number of ways to make sure no one reads your journals. the best choice would be to get a book to write it in, and hide it somewhere. but a fingerprint scanner seems like a good idea…
oh jeez… i need sleep… i’l be seing things up side down soon… 
If you are all so afraid that someone might read your DDs, just start writing in code. If you write something in your own code every day, you’ll eventually start reading/writing it fluently.
Also, it makes you look really cool if you have a book full of encrypted text on your bedroom floor. Your mother will think you’re James Bond or something… 
i don’t know if this was mentioned as i just skimmed through this, but there’s always the traditional under-the-floorboards/carpet. or my own favourite for small notebooks and diaries: inside stuffed animals. i have some left over from childhood still malingering in my room, so i made a slit in the bottom of one, took out some stuffing and safety-pinned it together again each time. sounds wacky but so far there’s been no trouble with my own parents, which wasn’t always the case when i chose more obvious hiding places.
hmm…maybe though, could i point out that asking yout mother not to read your diary is probably tempting fate? unless she bought the subject up. …
The simplest way (and cheapest) is to create a code. I remember creating one and it was stunningly easy. (Actually I created a shorthand for recording homework, but it was barely readable). Make sure you have a good cover-all, like leaving out every other letter in a word you don’t have code for.
I suggest getting a slip of paper and writing some connectives and coding them. For example, my “the” was a T with a line under the right arm, and my “questions” was a Q with a dot inside. My “in” and “out” were circles with arrows pointing in or out. Later I replaced the arrows with arrowheads and cut most of the circle out of the picture. I also used common shorthand like “2” and “U”, although I dislike them.
In later years, my teachers got pissed off and I had to go to longhand. I was stunned at how long it took to write .
It’s great fun and I seriously recommend it. Alternatively or with this, you can learn to write backwards. That isn’t much of a protection though - more against people being able to read a few words before you snatch your diary away.
[color=indigo]it’s hard to put this in here as it doesn’t match up, but the way me and friends used to write naughty things in class without the teacher being able to read it out to everyone else is to write like this
I aX
XnX
l i X
omX
v eX
e XX
X XX
It says “I love anime”
write from top to bottom, putting a X where a space should be. Easy. When it’s on paper it looks a lot better, and harder to read, sometimes even for yourself. Also, when there are more than three words it tends to be better![/color]
Yay, another anime fan I knew I liked you for a reason. 
[color=indigo]hehehe…hang on… 
…there are ppl who don’t like it?!
woah[/color]
one of my friends thinks that i’m crazy for watching anime. so it’s mutual, cause he is probably crazy too
but a code could be fun… perhaps i should make one? with my imagination i could probably make a code that even those fbi computers couldnt crack 
imagines Frequency analysis on a dream diary:
“Well, the most common word is ‘!!’ in code. That’s probably and, it, if, with…”
“Second, there’s “!K”, which is probably some connective…”
What were they actually? ‘Lucid’ and ‘False awakening’!
I’m sure I could crack your code, but it would take loads of effort. Truly.
I bet your mother doesn’t know 1337 5p34|<.
You could also propose a deal. If your mother wants to read your dreams, then she has to write down her dreams and show them to you, uncensored 
1337 5p34|< |5 @ G00|) Pr0-|-3<-|-!0||. ||0|30|)/ (4|\| R3@|) !-|-, |\|0-|- 3\/3|\| /0|_|R53|_F
(leet peak is a good protection. Nobody can read it, not even yourself)
j35 |_33+5|>34|< //0v1|) 1//o|37|) |33 1337 |=0|2 (0o|3
Yes, l33tspeak would indeed be l33t for code.
[color=indigo]1337 !5 345/ 70 |234| ) |3/ /0|_||2531|= |3|_|7 | )3|=!|\|473|_/ 600| ) 70 ||53 70 |-|!| )3 57|||=|=.
60 |=0|2 !7[/color]
l33t is easy to read by yourself but definitely good to use to hide stuff. go for it
Wow. I couldnt read it 
; im stupid. >> And I consider myself computer-wise. Heh.
see it aint that hard if you know what it means already, but if my mum read that she’d be like “omg…I think the computers broken…”
either hide your journal, perhaps between your matresses, or start using shorthand
for example, i would never write “my penis truned purple and then i had sex with my sister”
instead i would write, “part of my body turned purple, then my sister looked pretty and then something happened i forget”
but this is actually CODE because i will remember (when i read it with the rest of the dream), I will remember that i had sex with her. “something happened i forget” means i had sex with the character)
just be vague or cryptic on the embarassing parts.
I use the same kind of shorthand, partially because I fear someone will read my dream diary, but most of all because I’m so lazy.
If I dreamt that I would write something like: “pen. purple, s. sister”. On top of that, I tend to write with very tiny and unreadable letters when I dream of something I want to keep private.