Interestingly, in German, I've usually encountered "selten" as meaning "strange", although it can also mean "seldom".
Meanwhile, German also has the word "rar", which also (and only) means "rare". However, I've yet to see it used (though I'm not a native speaker and might be looking in the wrong places).
As for "uncommon", the best German translation is "ungewöhnlich". I wonder whether the Norwegian "unvanlig" is a shortened version of that!
Selten means rare (or uncommon) in German, as does rar. However, rar is rarely used. For strange, you could use the word seltsam, which you were probably thinking of. Merkwürdig (literally: worthy of remembering or noteworthy) is another possibility. As is komisch (literally: comical). Ungewöhnlich, which has the meaning of both strange and uncommon, is pretty much the same as the English word unusual (sich an etwas gewöhnen means to get used to something).