In the Paint.Net 4 the linguage files were in .ini and we copy one reneme it and open with notepad. The .ini file had "LANGID=2070", the number is the id of the language. The Paint.Net only had the id of the languages and we create and edit them. We change the id of lange to own language and translate the rest.
ex
LANGID=2038
[CommandsDataModule]
00000003=&Save
00000004=Save
00000006=Save &as...
then
LANGID=2070
[CommandsDataModule]
00000003=&Guardar
00000004=Guardar
00000006=Guardar &Como...
Done!
It is possible translate the program as we want.