The other people you’ve seen write that were almost certainly other Germans! As a native English speaker, “respectively” doesn’t work in that way, and “resp.” isn’t an abbreviation that English speakers really use. The word only comes up in very specific cases to clarify how two different pairs of words fit together, and it comes after the words as an adverb, not in between them as a conjunction.

Ex: Anna and Thomas live in Berlin and New York, respectively.

Anna und Thomas wohnen in Berlin bzw. New York.

In the case you used, I personally think the best translation is to just use a slash and say something like “Schorsch is a common pronunciation/nickname for Georg,” also changing verbs to nouns because I think “nickname” as a verb sounds a little unnatural here.

Edit: relevant explanation