The problem with online translators is almost all of them translate word for word, not the actual phrase. Keep in mind the way we word things in english is not how they may word them in european languages. Just as in same way we word english phrases differently region to region, state to state, USA v's UK or New Zealand, etc. and even differently between different social groups and people of different demographics. Also, not only different wording of phrases, but some other languages use different placement of adjectives and verbs etc. within the actual sentence.

I do not believe there is a perfect online translator. The concept is far too complex to be able to create them. Translating from or to English from french or german or russian or the nordic countries are usually the ones with the most mistakes with online translators in my experience.

At best you can hope for is at least understanding the meaning behind the sentence. And even then with the languages mentioned, some mistakes in meaning can happen as a result of the online translation.

Using a phrase book is probably the best option for obtaining more accuracy.