BackgroundThe standard procedure for building an app with a selectable language option is to have a set of files (a pack) for each language where the target string in the target language is referenced by a key. The keys are unique within each language pack and the same between packs.
These language packs could, for example, be in YAML files:
hi: Hello, world!es.yml
bye: Goodbye, world.
hi: ¡Hola, mundo!Ruby on Rails includes the i18n gem by default, giving us a very easy way to produce any snippet of language we need. For example, I18n.t "hi" would return the string "Hello, world!" if our environment is English, and "¡Hola, mundo!" if our environment is Spanish.
bye: Adiós, mundo.
If we ask for something that is not defined in our language pack, we get a message to that effect, e.g. "translation missing: en.seeyoulater". Note that the message includes the missing key ("seeyoulater"), so we can easily go in and add the necessary content.
The StoryIn a recent project, I needed to create an admin page which would allow us to identify content that exists in our main language (English) but not in our secondary language (Spanish). To do this, I needed a way to prevent i18n from generating the translation missing message and instead return something obvious, such as nil.
Fortunately, I18n#t provides an option to raise an exception when content is not found:
I18n.t "seeyoulater", :raise => truewhich can then be caught to give us our desired nil.
I18n.t "seeyoulater", :raise => true rescue nilProblem solved, job done.
OopsObviously I wouldn't be writing this post of that were the whole story.
My admin page worked perfectly on the development server, but on production it failed. The two systems are identical; what could possibly be the cause?
A little bit of detective work uncovered two points:
1. There's an i18n option, turned on by default in a production environment, to not generate "translation missing" messages. Instead, when looking for a translation of something that exists in the primary language, i18n will automatically and silently use the original string (e.g. English) in place of the missing translation.
2. This automatic and silent substitution has the unwanted side effect of pre-empting the :raise => true option above. Now our missing-translation detector is broken.
The symptom of the failure on production was that no translations were reported missing, and much of the content that claimed to be in Spanish was actually in English.
ConclusionIn the end, all is well. In the end, we didn't need this functionality.
But I'm bothered by the fact that the default behavior of i18n is to treat exceptions as things to be avoided at all cost. Obviously we don't want uncaught exceptions making their way into our error log (or worse yet, to the browser), but there are valid reasons for throwing and catching exceptions, even on a production server, and this is one of them.
I'm bothered that I've explicitly written into my code that I want an exception, and i18n is pulling rank on me and saying no, you can't have one.
In the end, though, the logical solution is that any translations that need to be managed from the web should ultimately be in stored in a database and managed along with the other dynamic content. Translation data that is stored locally, e.g. in YAML files, should be managed/tested on the development system.