Two marks, and why both are needed
The apostille was invented to replace a chain of stamps with a single slip. It works only between countries that agreed to trust each other's slips. Where a country stayed outside that agreement, the old chain survives untouched, and a British paper has to be marked twice before anyone there will read it as genuine.
Ethiopia's standing, and what it changes
Ethiopia has not joined the Hague Apostille Convention. A paper for Addis Ababa, Bahir Dar or Mekelle therefore requires embassy legalisation after the British mark rather than instead of it. Both marks matter: the consular officer looks for the British one before adding their own, so skipping a stage does not shorten the route, it stops it.
What the route costs you in money and days
Money is the predictable part. The British fee is fixed per paper and published, so you can total it before you start. What the consular side charges is set by the receiving country and sits outside anything quoted here, which is why a sensible budget treats the British figure as a floor rather than the whole bill.
Days are the unpredictable part. An apostille from United Kingdom to Ethiopia moves through the post, then waits in a queue that no British office controls. People come unstuck when they order the paper, the mark and the flight in the same week. Leave the consular stage room and the rest of it follows easily.
Amharic, and the papers that actually go
Public business in Ethiopia is conducted in Amharic, and English is common in trade and higher education. Where the reader is a ministry or a court, an Amharic version should accompany the file. Have it made once both marks are attached, so the translated set matches the bundle that lands rather than the plain sheet you began with.
The mix leaving Cardiff says a good deal about the connection. Development agencies, universities and aviation account for much of it, so qualifications and employment papers outnumber family records. Adoption and marriage files appear, and those are the ones where ordering a certified copy first saves a household from replacing something irreplaceable.