declension

Drone.io is cool, and free for open source projects too: (https://drone.io/pricing)

Yep, gettext has been working well for decades (and ported to many languages), though the syntax is a little clunky I find.

+1: OP probably should have checked the English grammar and spelling when writing about... grammar and spelling

Quod Libet [1] is a mature but "lesser known" audio project written in Python and GTK+ (3).

Whilst there are probably some quite high barriers to entry (the user community is very tech- and music-savvy, the project is fairly feature-complete, and the codebase quite complex), we're fairly welcoming and try to take care of our (large) backlog of tickets whilst welcoming useful contributions where possible, or at least discussing / explaining their considered rejection.

In particular, we could really do with a dev (or in fact buildmasters / testers) who are Mac-based ideally with some knowledge of building and testing Python and GTK+ apps on OS X. Probably best to email the list for further details.

[1] http://code.google.com/p/quodlibet/

Small title correction: "a tool that lets you"

let's == let us (contracted form)