In my experience online translations can be helpful but not always accurate.
I decided some time ago to buy the book editions of all dictionaries I would be likely to use.
If going down that road get yourself a good dctionary, for the sake of a couple of extra bucks it's worth it.
Another 'useful' site is:
http://dict.longdo.com/
English - Thai / Japanese - Thai / German - Thai / French - Thai Dictionary
Also, alot of translation websites all take their information from a central source so cross checking with 2, 3 or 5 translators will give you the same result, and not always the correct one...
Use all tools available to you to check the word, online / machine translation is just the first step.
German Ovt :
http://inventory.overture.com/d/searchinventory/suggestion/?mkt=de
Google trends:
http://www.google.com/trends
(It is helpful to use a German word you know to be 100% correct and compare your word with it. This will give you a more accurate reflection of whether its right or not. Enter both words in the search box seperated with a comma)
Search for it on Google Germany:
http://www.google.de/
Use the German Overture bid tool to see if it's getting any bids:
http://uv.bidtool.overture.com/d/search/tools/bidtool/?mkt=de
Finally, look for language forums and ask the members there to confirm translations.
You can offer to pay a few $$'s for a word list to be translated for example...
This is a good option as you will be dealing with people rather than a machine.
A lot of languages have subtle or not so subtle nuances that you wont know about, verbs, nouns, masculine / feminine / neutral, the context it is used in etc etc...