If you are submitting an apostilled UK document to authorities in a non-English-speaking country, you will likely need a certified translation of both the document and the apostille certificate. We translate both.
Almost always, yes. The apostille is itself a UK document in English, so when you're submitting it to authorities in a non-English-speaking country, both the underlying document and the apostille need translating into the destination language. We bundle both in one order.
The reverse case also comes up: a foreign apostilled document — say, a French marriage certificate with an apostille from the French foreign ministry — needs translating into English for UK use. Same workflow, different direction.