Text version explained how different characters use different types of speech in the manga. Genma, Soun, Cologne, and Happosai use a more archaic form of Japanese. Nabiki speaks in slang a lot. Ukyo speaks with a Kansai dialect (known as Kansai-ben) Japanese rather than a Tokyo dialect (commonly thought of as standard) Japanese. Ranma speaks casually and unrefined most of the time, rarely uses honorifics (though he does use them with people he respects, just met, or sarcastically) He occasionally will talk politely or even use all the proper feminine words/pronunciations while female. Chinese Guide spoke a mix of Japanese with Chinese liberally sprinkled in making him hard to understand. Shampoo did not speak broken up Japanese rather she spoke a mix of stereotypical Chinese person speaking Japanese and Archaic Japanese.
Text version explained more of the puns. Example: when Akane's hair is accidentally cut off there is a pun having to do with "kega nakatta" (she wasn't hurt) and "ke ga naku natta" (her hair went away). Another example is the Shi Shi Hadoken story line which was absolutely full of puns since the Japanese have a lot of puns that use ki. I could explain some of these puns but seeing how someone else has already done so I won't. Here is a quote on the Shi Shi Hadoken storyline (I believe that the original writer of this quote is Julio Gea-Banacloche but seeing as to how I can't find it on the net I am not positive.):
the entire story is constructed on puns, on various expressions involving the word "ki" (spirit)Text version had comments like this one to better explain what was happening from a Japanese point of view:
Specifically, part 4, where Ranma generates one type of floating "ki" after another, is just really a string of puns, the point being that what the floating "ki" does is connected, via a pun, to Ranma's frame of mind, is described by some set expression that has the word "ki" in it (this gives us the "ki" that will not move, the "ki" that scatters, the "ki" that loses its way, the short little "ki" (a pun on "short-tempered"), and so on. Not being a native Japanese I can't tell, of course, which of these puns are real groaners, but I suspect that most of them are.
And, in a sense, this is all just setup for the "ultimate pun", which comes at the climactic moment, in part 6, where Ranma figures out why Ryoga isn't hurt as the "heavy ki" (another pun, of course) comes crashing down on him. This revelation, which Ranma yells with a straight face and all the Furinkan high students echo with equally serious expressions, is again nothing more than a pun based on the word "kinuke" (dispiritidness, dejection) and the further meanings of "nuku"/"nukeru"/"nuki" (pull out, withdraw, extract; leave out, skip), including, specifically, the compound "surinuku"--which, again, you will not find in dictionaries, but which is not really a made-up word, I have seen it in other mangas to describe a "glancing or grazing blow, a blow that barely misses" (probably related to surimuku, to graze). Anyway, the point is that because Ryoga is "kinuke" his "ki" goes "surinuku"--and at that moment, which the Western reader would no doubt mistake for a highly dramatic moment, the Japanese reader is probably groaning and saying (the equivalent of) "oh, noo..."
In Japan, before you get married, you're supposed to sort out, tidy up, finish, etc, any 'hanging' relationships.In explaining what Soun said related to Akane and Ranma in the last volume.
An example of how the text version added detail was how it explained the narration at the exact end of the manga. Basically it used a sports analogy to say that Ranma and Akane's relationship has gone into overtime (or extra innings) and how Takahashi decided to have a less conclusive ending so that the fans could imagine what comes next. VIZ version ended it with the line "and so the game of love continues.
In the Text version/Original Japanese Ranma is much more witty with better comebacks. In an interview Takahashi mentioned that she read a lot of Spiderman when she was younger and it influenced her writing of Ranma. So imagine Spiderman type comebacks to get a better idea of Ranma's. (Other aspects of spiderman are in the manga as well for instance Ranma's sitting positions - hanging upside down, Ranma's crawling on walls and ceilings, and Lucky's glue/ink attack is very similar to spiderman's webbing).
Since females and males in Japan speak using different words much of the time. Female Ranma's jarringly male speech is not really shown in the American version. So Ranma in the US version comes off as being pretty much a normal girl where in the Japanese version his girl form is a super tomboy (except when Ranma wants to come off as a normal girl - around his mom and fooling people, or super cute - to get stuff, or desirable girl - to get stuff).
Another thing mentioned in the text translation but not shown is that in the original Japanese - Ranma is shown being very polite (uses all the proper honorifics for example) to the Tendo's at first but loses them as they insult him.
Other differences are some times things would be shortened or changed to better fit the word bubbles, Ex. during Umisenken story arc we are told that the old house was torn down and Ranma's mom moved there. In the Japanese version it gave more information in that she said the poor tenement house was torn down so I moved here. This tells us more information in that we know they were poor whereas the English version it is not stated.
Things were added, things were changed to make it easier for English people to understand such as Japanese sayings, and things were changed because they wouldn't make sense without further information such as puns like Ryoga's dogs name.
For the most part the changes in translation do not overly change the storyline or make sense since it is being made for a different audience but occasionally the translation was wrong in a way that changes the story some.
The picture on this post is taken from the Ranma manga. What a lot of Westerners might not know is that the picture in the background is a reference to a famous Japanese work of art Wind God and Thunder God (Fuujin Raijin zu Byoubu) by Tawaraya Sotatsu. Edo Period (17th Century).
This website gives further information on the differences between the very first Ranma manga in English and in Japanese. http://www.zompist.com/ranma.html Less on the difference in translation but more on the differences in quality.