I'm looking for a German to English dictionary which for example, when I search for the word "Wörterbuch", it shows:
Is there anything like this?
Such a dicitonary does not exist to my knowledge but you can easily get there with the wordformation browser offered from Canoo.net.
If you search for Wörterbuch click on the Wordformation button there. Then you are presented with an analysis as follows:
The blue entries are clickable, which means you can click on Wort and on Buch there. You will then not only find all other frequent composites built on these words but you will also have a link to a very concise German > English dictionary on the top right corner of the screen named LEO (DE-E) for your convenience.
The search you are looking for is not displayed at once, but it is only two mouse clicks away, which is better than nothing. This can be done for many composites but as is the case for most dictionaries only the most frequent will be includes.
You are looking for a dictionary of German stems. Such dictionaries exist, but they aren't targeted to language learners but linguists.
But seriously, you don't need such a thing. Your goal is identifying the parts of a compound. There's an easy way to to that: understand the compound from the end backwards.
So … a Wörterbuch is a special kind of Buch. That's the logic behind German compunds. Let's check the rest.
Continue with the rest
Hmm. No luck with Wört. It may be plural then. Plurals often have those pesky Umlaute in there. Look up Wort instead. YES!
BUT, the dictionary says the plural of Wort is either Worte or Wörter. So, the er we stashed is part of Wörter. We are done.
Wörterbuch → book of many words.
This may seem tedious at first but believe me it works automatically as soon your vocabulary grows. Your lectures are built that way the compounds are made from words you already know. It's the same way German children learn the language.
If you are curious. There are some compounds which leave you clueless. And German speakers, too. For example Staubecken. This is either
die Staub-ecken (multiple corners filled with dust)
das Stau-becken (a basin meant to pond water)
Context is key then.