The lang files for the dojo strings are in the folder:

phpr/Default/nls/

Default.js contain all the default strings (English)

And each folder contain the translations:

phpr/Default/nls/es/Default.js -> Spanish Translation
phpr/Default/nls/de/Default.js -> German Translation

For use the translated strings, just use the global var nls:

phpr.nls.TEXT

Where TEXT is defined in the Default.js file.

You can also make the translated string like:

"invalidUsername": "The username \"%s\" is not valid"

and then for use it:

phpr.nls.invalidUsername.replace("%s", value);