Can translation documents filed in the grant procedure be reused?

Yes. Translations of claims into the two EPO official languages other than the language of the proceedings that were previously submitted during the EPC grant process can be reused for filing the request for unitary effect. However, you must refile those  translations of the claims.

Similarly, where the language of the proceedings is English, patent proprietors who choose to file a translation of the European patent specification into an official EU language other than French or German are often able to use an adapted version of an application first filed with a national patent office. Additionally, translations of specifications prepared for validating a European patent in states not participating in the Unitary Patent scheme can also be reused.