[According to Wikipedia][1] and Oxford dictionary, the correct translation for "seasonal-adjustment" is "Saisonbereinigung".

I am not sure about "seasonal-differencing". As stated by @jarnbjo and DeepL Translator, it seems to be "saisonale Differenzierung". I do not know much about the context, but if you explain it, I could try to find a better translation.


  [1]: http://de.wikipedia.org/wiki/Saisonbereinigung