Add basic translation tests

[rpkilby]

Test for #5696.

This PR is based off of the commit that adds the dist build, which doesn't include the fix from #5696. Running the tests locally, this fails. However, Travis creates a merge commit from the current master, so this passes in CI.

[rpkilby]

One thought - I'm not sure if translation tests will interact poorly to potential message changes and our use of transifex. As an example, let's say the exception message for the standard APIException is changed from "A server error occurred." to "An internal server error occurred.". This change would result in a test failure, since there's no corresponding french translation for the updated message.

Would we just need to temporarily fix the translation files, then ensure that transifex is updated as well?

[carltongibson]

My thought for this was just to do some kind of find... on the dist build to make sure the file is there. ???

[carltongibson]

I think we should have this. I would have caught the issues with the 3.7.4-.7 releases.

If the test proves fragile we can adjust the strategy. (It should be fine though...)