Text translators aren't reliable because of the construct of language. Languages are made up of more than single words with single meanings. Words in some languages can have more than one meaning and words put together in phrases can change the meaning of the words. So, we have three issues with text translators: multiple meaning words, context, and idioms. So far, the text translators are not sophisticated enough to recognize these issues.
The other problem that text translators run into is regional peculiarities. In some languages, a word will have one meaning in one region and another meaning in another. Take, for example, the English language. Two of the countries that share this language are England and the United States. And yet, the words in the languages may have totally different meanings. In England, describing the rear storage area of a vehicle, the word is "boot," but in the United States, the word is "trunk."
Your best bet for translation is someone who is actually versed in that language.
I know from experience that text translation engines are not reliable. They often give incorrect usages of words or put words together in ways that are never used in the language that the passage is being translated into.
The main reason for this is because it is hard for a machine to determine the sense in which a word is being used. If a word has many possible usages, the computer program must pick which one is correct in a given context. This is especially problematic in cases where words are used figuratively. It is extremely difficult to construct a program that can do this accurately.
I know for a fact that at least 99.9% of them are NOT reliable, especially google translate. Online translators translate by each individual word, so if you have a paragraph or even sentence it wont give you the exact definition. So when you read the definition it wont make sence, just a bunch of gobbly gook. I know this because I know Chinese and I tried using it and it came out totally wrong. If your doing this for some kind of language class, I would just try to figure it out with out the computer, IT WONT BE ACURATE!! :)