Many translators aren't comfortable with editing source code. They want to get a file, e.g. in XLIFF format [1], which they can then load into their translation management system, and then use a GUI or web based tool to enter the translations for each string, and then at the end export the updated file and send it back to the developers. Plus, the translation management system makes it easy to keep track of progress (what % of strings have been translated so far), automate review (require each translation to be signed off by a second translator), etc – but, translation management systems can't import/export source code, but they often can import/export message catalogs.

[1] https://en.wikipedia.org/wiki/XLIFF

I wonder if you could create some kind of domain-specific language that would be easier for a translator to interact with, without said translator needing to understand the nuances of the underlying programming language, or deal with anything more complicated than non-nested if/case statements.

The ICU project does that: http://userguide.icu-project.org/formatparse/messages

None of my translator friends has had anything good to say about those tools, though admittedly I know a small skewed sample of more technically-inclined types.