Arabic takes more room

The layout is designed in English and the Arabic arrives afterwards.

That order is the whole problem. The grid, the type size, the length of the line and the space between the lines were all settled by an English word count. Then the Arabic comes back and it does not fit, and the fix is always the same three moves: drop the point size, tighten the leading, shorten the line.

Arabic needs the opposite of all three. The strokes are finer, the letterforms carry their meaning in marks that sit above and below the line, and at the same nominal size the script reads smaller than Latin type and needs more height, not less. Close the leading and the tails hanging under one line meet the line beneath it. A measure that is comfortable in English is cramped in Arabic even when the word count came back lower.

So the page ends up with the English generous and the Arabic squeezed. Nobody decided that. It is what happens when the first language is a design and the second one is a task. On the worst version both sit in the same frame, English at a size somebody chose and Arabic at a size that was left over.

The reader can tell. Not consciously, and not in a way that ever comes back as a comment. But a page tells you who it was made for by where it has room to breathe, and across most of this region the language on the tight side is the one most of the market actually reads.

Write the Arabic first and set it first, then fit the English around it. English gives up very little by going second, and it is the only order that ends with both languages readable.