The benefits of translation memory tools such as Trados for translating are numerous; but they have their negatives as well. They encourage the translator to translate everything on a sentence by sentence basis. Every source sentence will have a corresponding target sentence. It is not always ideal to translate in this manner.
For example, consider the following Japanese sentence and its translation:
I like sushi. However, I cannot eat sea urchin.
Notice that in Japanese it is natural to say that all in one sentence. English on the other hand works better as two sentences.
If you translated that Japanese sentence using Trados, you can split the English translation into two sentences. However, if you use that translation memory for translating English, you will get no matches for the sentences I like sushi, or However, I cannot eat sea urchin. You would have to know to expand the segment to span two sentences.
Translation memory CAT tools like Trados encourage you to translate with a one-to-one correspondence so the translation memory is useful in both directions. It is wasteful to misalign sentences because the resulting TM will not work if the language direction is reversed. Therefore, a translator using Trados will probably translate the above sentence as I like sushi, but I cannot eat sea urchin. This sentence is fine by itself, but it doesn’t have the same impact as separating them as single ideas.
This is just a simple example, but the problem is much bigger than style choices. When using Trados, you translate entire paragraphs line by line. Every source has a matching target. However, the way you organize a paragraph and express an idea in one language, may not be the same as in another language. But with Trados, you don’t have that freedom. You are given a sentence to translate, and then another, and another. You don’t have the freedom you would if you were translating by hand. If you choose the expand the source segment to encompass the entire paragraph, you have essentially made that segment worthless with respect to the translation memory.
Trados and translation memory CAT software are great tools, but they encourage translation of single sentences, rather than ideas or concepts. A test often used after a translation is to run the translation memory that was created against the original source document. You expect to get 100% matches for the entire document. However, a good translator will not translate everything line by line with one-to-one correspondence between source and target.
Translation is more than converting a sentence from one language to another. It’s about expressing something naturally in a different language. CAT tools like Trados don’t encourage the natural translation of ideas, but rather the conversion of sentences.