The Text in the Word Bubble

I’ve been thinking about word bubbles lately, specifically the conventions behind how words are organized in them across Japanese and English.

Basically, if you ever look at a word bubble from an English comic, be that a translated manga or something originally created in English, the words tend to follow the shape of bubble to an extent, such that the top and/or bottom lines of text are shortest and the middle bulges out. In contrast, if you look at manga in Japanese, the text is usually in the shape of a square block, though it might be more accurate to say that the text is “top-justified,” where the top of each line is flat (remember that Japanese text in bubbles is generally written from top to bottom and from right to left), and the length of the final line can vary from being the shortest to being the longest. They don’t necessarily have to be this way, as is evidenced when an English-language bubble in a Japanese manga ends up having the text un-centered, but these seem to be the “rules.” When we defy them, something looks “off.”

What I’m wondering is, how much of this is the result of the written languages themselves, and how much of it has to do with the conventions laid before us by decades of comics? Could it be that a stable top is more important in either case, but that the top line in an English text is always flat due to the horizontal nature of English writing, whereas Japanese has to make an effort at it? Is it simply efficiency, or the result of past limitations which have seeped into the very nature of how we perceive word bubbles? What about other languages, notably Hebrew or Arabic which are horizontal and written right to left? How do their translations/comics fare?