There are many alternatives to Better PO Editor for Mac and since it's discontinued a lot of people are looking for a replacement. The best Mac alternative is Poedit, which is free. If that doesn't suit you, our users have ranked more than 10 alternatives to Better PO Editor and four of them are available for Mac so hopefully you can find a suitable replacement. Other interesting Mac alternatives to Better PO Editor are Virtaal (Free, Open Source), BabelEdit (Paid) and Xliffie (Freemium, Open Source).
Poedit is cross-platform gettext catalogs (.po files) editor. It is built with wxWidgets toolkit and can run on any platform supported by it (although it was only tested on Unix with GTK+ and Windows).
Virtaal is a graphical translation tool. It is meant to be easy to use and powerful at the same time. Although the initial focus is on software translation (localisation or l10n), it can be useful for document translation.
Xliffie is designed for developers in mind, with functions like checking printf-formatted string (make sure your %@ is not a %d in the translated string), search with regex, Google / Bing translated, etc.