The web offers many kinds of specialized dictionaries. Most of these don't have the gravitas of traditional heavyweights such as the Oxford English Dictionary, but that's no reason to ignore them. Within their specific niche, specialized dictionaries can be very useful.
Sometimes you want to know how a certain word translates into other languages. Rather than looking up each translation one by one, you can use a service that—on one page—shows how a word translates into many languages.
A multi-language translator is available at the Logos Multilingual Translation Portal. Suppose you want to know how the word red translates to other languages. Enter the word red and select English as the source language. Leave the target language and the other fields blank, then click Search. You will see dozens of languages—although I was a little disappointed not to find Tok Pisin amongst them.
For each language a translation is shown, together with an audio file in many cases. You can even enter idioms (such as heads or tails) and other short phrases, although as your sentences get longer the number of matches decreases.
Multi-language translation is also provided by Wiktionary, but it's not displayed by default. Open a Wiktionary page (such as the one for the word red). Scroll down to “Translations” and click “show” for the meaning that you want translated. You will then see the word translated to many other languages.
Again, I didn't find a translation to Tok Pisin. But there is one now! Because this is Wiktionary, I was able to edit the table to add the translation myself.
In the reverse direction
You can also go the other way, to see what a word means in other languages. This is Wiktionary's default view, so it's entry for rot shows that this word means red in German, but it means decay in English and Dutch, and it means belch in French and Catalan. So maybe Rot is not the best international trademark for your red product!
You can also use Google's “define” feature. A Google search for define:rot shows links to various dictionary definitions (including for proper nouns and acronyms). At the bottom of the page, click all languages to see what rot means in the other languages for which Google has links.
PS: Thanks to davidsarokin for bringing the Logos portal to my notice.