A feature of specialized texts is that many fragments of the text are often duplicated. They can be single words, phrases and even whole sentences. When you repeat the natural course of action is to copy the earlier translation to a new location. This can be done manually, but it's better to facilitate this process. That's the purpose of these programs to assist translation. CAT (computer assisted translation) - these tools memorize the already translated text by associating it with the source text. In this way, we create a database containing pairs of translation units (usually whole sentences) in two languages. When the program finds the text that was once translated, it automatically inserts it in the translated text to accelerate the translation process
There are many CAT programs on the market. They all work more or less according to the principles described above, but of course they may differ in details and offer different features. For instance some programs, such as Wordfast, work as the attachments to the editor, Microsoft Word, while others, such as Trados package, can act as the separate tool, but they also offer self-editors (eg. TagEditor). The most popular CAT tools include SDL Trados, Wordfast (previously free), Déjà Vu and OmegaT (free). Obviously this is not a complete list, but only a few of them.
Before you buy one of them, you have to realize that CAT programs do not perform translations, but only substitute the fragments of the previously translated text by the translator. Therefore, their actions should not be referred to as the so-called “machine translation”, because, in fact, a translator performs the translation, and the programs are intended only as a supporting tool, like a word editor or computer dictionary.