So what's for [dessert] tonight?

dessert pudding afters

Info: Both "pudding" (in this sense) and "afters" are unknown in the US.

The mice have been [knapra] at the furniture stuffing.

Hint: Use the progressive form!

nibbling

Info: "Gnawing" is more for wood or hard food.

They bought the house incredibly [billigt] .

cheaply cheap

Info: Both "cheap" and "cheaply" work here.

The key [brist] in the plan was the lack of feedback.

flaw deficiency imperfection shortcoming defect failing

The contract becomes null and [ogiltig] if either party violates the conditions of Section 5.

void invalid

Info: "Null and void" is a standard legal phrase.

They tried to [klistra] the pieces together again.

glue paste mucelage

Info: For paper (as in schools) paste and mucelage are possible alternatives. Glue (including epoxy and similar compounds) is appropriate for a wider range of materials, and for metaphorical uses.