Online editing gettext files?
I used SimplePo recently, works great. You need to export the edited .po file then use command line gettext tools or POEdit to build .mo.
The Ubuntu launchpad service has a subproject "Rosetta" which provides such a tool. You could install that on your server: https://launchpad.net/rosetta
There are also:
- Kartouche
- Pootle
- TCKTranslator
This question is high on Google and the answer is a little dated. I found http://poeditor.com/ an excellent resource. It is a free website, it is very easy to get started, you can invite translators and they have a credit system where you can use automated translation tools for your strings to help you get started.
Very slick, very easy.