Non-defining relative clauses.
Non-defining relative clauses are special cases of parenthetic phrases. Note the difference compared with relative clauses that define the preceding noun phrase (i.e. ‘the translations’ or ‘the translation in the tray’ in the examples below):
The translations, which have been revised, can now be sent out.
(added detail — they have all been revised)
The translations which (or better: that) have been revised can now be sent out.
(defining the subset that is to be sent out — only those that have been revised are to be sent out)
Note also that the use of ‘which’ in defining relative clauses is often considered to be stilted and overly formal. ‘That’ reads more naturally. It also helps make the meaning clearer, reinforcing the lack of commas, since it is used as a relative pronoun only in defining clauses. Unlike ‘which’, however, ‘that’ needs to be close to the noun to which it refers...