This is not a repost on this site as far as I know. Please read the whole thing before flames. I did not search other sites, but I'm pretty sure this will be the first. (if it isn't, i apologize)
There are a lot of threads that talk about how to talk to the horde or alliance via the use of number and letter combinations. I will only show the conversions for A-Z here to start. If you want to make complex sentences search around.
Ally = Horde
oeoyyeoyoeooooyueyyyyyyyoe
A = O
B = E
D = Y
P = U
Horde = Ally
ggoloaoolnlnaolngnnlllanog
A = G
C = O
D = L
F = A
J = N
Now here's the fun part. Download this: LessThanThree | World of Warcraft Addons | Curse It's called LessThanThree and allows you to put symbols into chat.
I decided to test if I could link symbols to horde, but when I did I got extra letters I had not seen before. (I tested every button on the add-on, this is the summed up results) Here are the conversions:
Ally = Horde
Single Note/Heart = V
Double Note = L
Spade = M (<---not to be confused with club)
Diamond = A
TM = H
Horde = Ally
Spade = M
Diamond = K
TM = R
So in total here is the summary of translatable characters you can make on either side:
Ally = Horde
A = O
B = E
D = Y
P = U
Single Note/Heart = V
Double Note = L
Spade = M
Diamond = A
TM = H
Horde = Ally
A = G
C = O
D = L
F = A
J = N
Spade = M
Diamond = K
TM = R
Sadly, the alliance can make a lot more actual (or readable) sentences with the available combinations. I have not tested combining two symbols in one spot to make more letter conversions than those found within aa-zz etc.
If you are alliance, here are some fun things you can say:
Hello my lovely moomoo.
May me have ale?
Me never love you. (ag zz fff ee oo d a p)
Me love you lon time. (ag ee oo d a p 700 ba ag)
Me lonely. (ag 700 b doublenote d)
If you are horde, here are some minorly useful/useless things you can say:
No Gank
Lag
Llama
Edit: If you know how, you can also edit the functions and visuals of the buttons in the LessThanThree add-on to show the letter you wish to make and have it send the appropriate key. You can also make it add spaces after each letter for you. Me and a friend did this with ours a month or so ago.