<p>How do you keep the spoken languages strings in your program up to date?
Is there an inexpensive way?  Where can you find people to do the conversions over time?</p>

There are companies which will translate resource files in the standard formats for fees; I think that's how most large companies do it.
I asked a similar question recently
here
about the best way to structure code in a project to support this, with my additional desire to preserve the readable strings in code. This is not standard, though... usually you would put all the string resources into a separate file and refer to them by ID in the code, and have the file translated.
See .rc files for Windows C++, .resx files for .NET, not sure what exists for Linux/Mac/other, but I'm sure there are equivalents.