The language Kuwait asks for
An Arabic text is required for papers used in Kuwait. That is stated plainly because it decides everything else: what you buy, what it costs and how long the file takes. Nothing about the paper's own language changes the answer, and nothing about who issued it does either.
The destination picks the language, not the paper
People reason from the wrong end. They look at the record in their hand, see that it reads perfectly well, and conclude that no translating is needed. But the reader is in Kuwait, and the reader works in Arabic. A record written in English, Polish or Urdu all land in the same place: each one needs Arabic sheets before anybody there can act on it.
Reading it that way saves a lot of guessing across a mixed file. Whatever the papers are and wherever they were issued, one target language covers the lot. An official Arabic translation in Edinburgh is bought for each of them in turn, and no paper in the folder is exempt because it happens to be readable here.
What Kuwait accepts on the Arabic pages
Kuwait takes a certified translation of the kind consulates and ministries accept, produced by a certified Arabic translator who signs for the work. No court appointment stands behind that signature, and no separate body has to countersign the sheets. The translator's credential is the whole of what gives the Arabic pages their standing.
Keep those pages with the record they were made from. A certified translation for Kuwait is read against the paper it came from, so the two belong in the same envelope and in the same order they came back in. Handing over Arabic sheets on their own leaves a reader with nothing to compare them against.
Per-page cost and turnaround
About £25 covers a page. Standard work runs 3–5 business days and the express route 48 hours, which is worth knowing before a date is fixed. Because the figure follows pages rather than subject matter, a short civil entry costs a fraction of a long agreement going in the same file.
Notarisation can be added when someone has asked for it by name, sitting on top of the translator's signature rather than replacing it. Most files travel with the signed Arabic sheets alone, so the arithmetic usually comes down to page count and which of the two speeds you pick.