I've discovered a great way to test my German knowledge (and really any language) and build vocabulary. Use random sentence generators to either translate from your native language or from your target language. It has helped me a lot! Especially saying my translations out loud. That way I work on my speaking skills as well. Here are links to various sentence generators in various languages:
Spanish: I couldn't find a good one specifically for Spanish for some reason :/ see below though!
Portuguese: I couldn't find one for Portuguese either! Ergh but still see below!
Dutch: http://bullshit.takovermeulen.eu/ (this one is funny xD)
Here is one for a bunch of languages! You can also test yourself and see if your translation was correct: http://www.smartphrase.com/cgi-bin/randomphrase.cgi?german
I hope this was helpful! Happy learning :)