I don't think this will serve as a translation of "claudicante" in all legal contexts, but in the case of contracts I believe this is what it means.

"Nulo" is void. "Claudicante" means that the contract is valid but that one of the parties can impugn it and rescind it, in which case it becomes void. This means it's voidable. So for practical purposes I think "claudicante" means "voidable".

"Contrato claudicante, susceptible de impugnación por las personas legitimadas, pero que ha empezado a desplegar su eficacia."
https://books.google.es/books?id=Ynx-JRBBWVMC&pg=PA13&lpg=PA...

"Durante la fase provisional, la doctrina tradicional considera el contrato anulable como un contrato de eficacia claudicante. El contrato se ha perfeccionado, puesto que reúne los requisitos del Art.1261 Cc, pero frente a cualquier pretensión de eficacia puede ejercitarse la acción de anulación u oponerse el carácter de anulable por vía de excepción."
https://www.notariosyregistradores.com/opositores/registros-...

"Voidable, in law, is a transaction or action that is valid but may be annulled by one of the parties to the transaction. Voidable is usually used in distinction to void ab initio (or void from the outset) and unenforceable."
https://en.wikipedia.org/wiki/Voidable

"Voidable contract: A voidable contract is a valid and enforceable contract which one party has the right to nullify (or, in [UK] legal language, 'avoid'). If he exercises that right the contract is then void with retrospective effect, as if it had never existed."
See also the paragraphs on void and unenforceable contracts here.
https://books.google.es/books?id=EKw3cYLg4yUC&pg=PA206