Well, that's what the setup I have does, almost. If you consider .po/.pot to be a unified format file. I extract the original texts, comments and internal names from the resx into a .pot (Portable Object Template). This is then sent to a translator-centric web site service. A translated file is then exported, although I export it as a .po file, and then use a library and a little bit of my own code to implement an IStringLocalizer. As someone said elsewhere, more and more services do support .resx directly, so I could consider skipping the .po handling in my code, and just use the .resx.

As for bloat, I find the .po format to be quite bloated, with it's use of the full texts as keys in each and every translation. I don't really like that, but in practice it appears to be working well and has been for many years. Then again, the obvious choice today would be json.