"wieder" and "weder" are not pronounced the same - also not on dict.cc (at least in the examples I've checked).
Depending on your mother tongue, there is a good chance that you cannot hear the difference yet if you've just started out learning German. In my experience, this is quite common when learning new languages. You will likely hear the difference after practicing and listening to the language for a while.
The "ie" in "wieder" is pronounced /iː/, while the "e" in "weder" is pronounced /eː/, if this is any help. You could also have a look at the linked Wikipedia entries (click on the two IPA symbols).
If you are interested in the IPA of individual words (as indicated in the comments), you could try the PONS dictonary (I am sure there are others).