Here’s a severance clause (severability clause, saving clause) from Mark Anderson, A-Z Guide to Boilerplate and Commercial Clauses:
If any provision of this agreement is prohibited by law or judged by a court to be unlawful, void or unenforceable, the provision shall, to the extent required, be severed from this agreement and rendered ineffective as far as possible without modifying the remaining provisions of this agreement, and shall not in any way affect any other circumstances of or the validity or enforcement of this agreement.
Plenty of other examples can be found online for harvesting elements to translate a German salvatorische Klausel.
The courts won’t always accept the clause, but it might help, for instance, where an employment contract has a clause in restraint of trade governing post-termination work.
I found salvatorische Klausel in the small Langenscheidt-Alpmann dictionary but not otherwise. Maybe that’s why DE>EN translators are always asking what it is.
Some clauses add nothing to the provisions of the Civil Code, but are harmless.
Anstelle der unwirksamen Bestimmungen gilt eine angemessene zulässige Regelung, die den angestrebten wirtschaftlichen Zweck weitgehend erreichen.
is apparently known as geltungserhaltende Reduktion and is NO GOOD. Consequences here.
Of course, this doesn’t relieve us from translating them into English.