Hello, if I may suggest, regarding a single .po file you should agree on some kind of translation rounds because .po files are not especially easy to merge. What I mean is e.g. Arturo's team will work on the file for one day, then he'll upload it to Launchpad. Then Waluyo will take over the translation for one day, review what has been translated, add his own translations and upload the file and so on. Meanwhile the other translator can concentrate on secondary things like the installer and tutorials.
I have also found translator comments a useful tool in this kind of team work. You may agree on some conventions regarding marking strings fuzzy (i.e. translated, not peer reviewed) or adding this information into comments so such unreviewed strings are easy to find.
Hope that helps a little. Good luck!
Please make an agreement about some early version of the file and let me know so I can commit it.
Regards, ~~helix84