One mark, and why that is the whole story
Two systems exist for proving that a foreign signature is real. Under the treaty route a single slip does the job, and every state inside the treaty honours it. Under the older route the receiving country adds a mark of its own on top. Bahrain sits inside the treaty, so your file meets one office and then stops.
Bahrain's standing under the Convention
Bahrain joined the Hague Convention in 2013, and Britain has been inside it far longer. When both ends of a route are in, the apostille is sufficient on its own and no consular officer enters the picture. That one fact decides how long the paperwork takes, how much of it there is, and what you end up paying.
The Cardiff to Manama route in practice
The British side is a single office for the whole country and it acts only through the post. It marks register copies, court copies, and papers signed by people whose signatures it already holds. No desk in Wales handles this, so the journey is an envelope and a wait rather than an appointment in town.
What makes an apostille from United Kingdom to Bahrain quick is the missing second queue. The paper comes back marked and is ready to fly. Your time goes on choosing the right version of the record in the first place, not on waiting for a consular officer somewhere to reach your file in a pile.
Arabic, and the files that actually move
Public business in Bahrain runs in Arabic, though English is common in trade and finance. A marked English paper is often read as it stands, and an Arabic version is added when a ministry or a court is the reader. Order the words after the mark is on, so the translated set matches the finished bundle rather than a bare copy.
The traffic out of Cardiff leans professional. Health, education and finance recruit from Wales, so degrees, registration certificates and police records dominate the post. An energy or building firm setting up locally sends its company papers. Marriage and birth records follow a residence permit, and those are the ones worth ordering fresh from the register office.