Comment 9 for bug 626015

Hello Amir, the girls and guys at Dalton Maag should be able to give a more authoritative answer but to sum it up, the rhythm is the "quick-quick-slow", or evenness of the type when read.

Speech has a rhythm, sometimes it is very measured and even: always. on. a. beat.; …and-at-other-times, it-can-fall-and-rise, as-poetry-forming-on-the-page, disjoint-with-surprise!…

With a general-use typeface, the aim is normally for a even cadence/rhythm, each letter and each word appearing where expected and sliding past the eyes without causing a jump in concentration. Various special-use typefaces may try and do the opposite.

If you're after a more academic overview, a Google turned up an essay on the following page:

  http://www.typeculture.com/academic_resource/articles_essays/ ("Rhythm in Type Design")

To your question about the .ttfs and about Launchpad. Rosetta is the translation part of Launchpad (as is "Rosetta Stone") and is separate form the bug tracker.

If you are able and would like to alpha-test either the Arabic or Hebrew then there are separate half-finished .tffs that I can send you. I'd certainly be very interested in feedback (although note that they are half-finished and lack diacriticals/vowels).