\"Voices\" and accents can be easily RolePlayed. Different ways of speaking and emphasising certain aspects of the language can be picked up and learned with little effort.
I completely adore playing characters with marked accents, or with a noticeable twist in their speech (Overly complex like a Renaissance fop, or excessively simple like the Half-Orc next door with an intelligence score of -3

). They tend to stand out due to people being subtly encouraged to focus on the text a bit more. But I do not think it would add much in game depth to force everyone to type constantly and permanently with an accent. In fact, it would drive them bonkers.
And I do not think a code for an accent is particularly feasible, it would necessarily be limiting and unrealistic due to its mathematical nature. A language, on the other hand, is more resembling of an organic entity of its own, and does not respond to such firm structures.
If you want to play the Dwarf with the stereotypical accent, more power to you. \"How be ye, lad? Thet would be good, aye! Oy, we gots ta help tha others!\". Or come up with new and different accents for the other races.
Racial languages, however, are an entirely different issue, and the developer team should consider if it is in theme to welcome their presence. Given the heterogeneous origins of the different cultures, it would not be far fetched at all to build a language system.
I have seen in a few online roleplaying games a different method that instead of scrambling letters according to a skill level, it handled the code much differently.
Each letter of the alphabet would receive a \"difficulty value\", that is, the difficulty to recognise the sound. Vowels and the most used consonants would be set to a lower difficulty level, whereas more esoteric characters such as \"x\", \"k\" or \"w\" (for example) are not as easy to pick up for a language student.
What the skill rank in a determinate language does (Say, Language: Elven = 30%) is to set a maximum of comprehension for the difficulty of a word. With 0% having a comprehension level of 0 and 100% an infinite value (You understand everything fluently).
So...how do you decide on the difficulty level of a word? Simple: You add the values of the individual challenges of each character (We will call that value DC from now on, for Difficult Challenge).
Example:
My character has 35% proficiency in the Dwarven tongue.
35% equals the ability to comprehend words with a DC equal or inferior to 20.
Well, let\'s see how that works.
Let\'s take the word \"Hello\". Supposing that the letters have the following DCs:
H = 5
E = 2
L = 3
O = 2
Then the word would have a DC of (5+2+3+3+2) = 15
My character would not receive the word scrambled, he would understand the meaning.
However, if a Stonebreaker comes up and says \"Morning!\"
M = 4
O = 2
R = 4
N = 5
I = 1
G = 6
Then the word has a DC of (4+2+4+5+1+5+6) = 27
The sounds are too complex for my character to understand.
Of course, the code would do all the math automatically, and filter in a blink of an eye which words we understand and which are way too difficult for our characters\' intellect.
It may seem a bit complicated at first glance, but the code is simple, and effective. It does not scramble random letters (which often results in awkward and unrealistic lectures), in opposition it filters complex words from more common ones depending on which letters compose them.
What do you do with the words that are NOT recognised, you say? Well, it is even simpler. The staff comes up with a list of say...fifty to a hundred sounds typical of the language. For example, we want the Elven language to sound very melodious and easy to the ear. So we propose sounds such as:
aelrir
moriebendir
salieras
leliomen
orie
ad
Etc, etc, etc. After we have a good number of made up words in the pool, we simply ask the code to randomly replace the non-recognised words for one of the fake words. I assure you, reading a scrambled text composed of only 100 words has enough variety to look realistic.
Anyway, that is my proposal for a language system. Do not ask me to write it any tidier and in detail than this

I am no coder, so this is as far as I can go.
- Golbez