Message translation package

[seankross]

Many folks on the Internet asked me if they could translate swirl's menus, which are just calls to message(). I was wondering what this community thinks about a package, a potential devtools feature, or a document with general guidance for managing message/string translations in a package. These are the concerns I had when implementing translations in swirl:

• Translations have to fail gracefully. If there isn't a translation for a string that string should at least be "produced" in English.
• The English strings should stay in the code in order to keep the code readable, as opposed to having some mapping between arbitrary keys and strings.
• Constantly wrapping strings in functions seems prone to introducing errors (have you ever misplaced a parenthesis when building a shiny app?)
• Translators may be experts in the languages they speak, but they're not necessarily experts in R package construction, version control, dealing with encoding issues, etc. The barriers to providing translations should be low.

The approach I took in order to address these issues in swirl was to create a function L() that produces a potential translation from a string, and then to create a binary operator %:% that takes L() on the left hand side, and a string to be translated on the right hand side. The %:% operator returns either the translation or the string from the right hand side verbatim if no translation exists. When it's all put together the code looks like this:

message(L()%:%"Hello world!")

Volunteers have been writing translations inside of .yaml files. The syntax for yaml is pretty intuitive:

"This is a sentence in English":
 "Esta es una frase en Español"

Each yaml file is read in as a list() and each list is stored in R/sysdata.rda. The L() function references these lists for translations.

This is just one idea and I'd love to discuss any other approaches.

[leeper]

This infrastructure already exists in R in the form of gettext() and ngettext(), though the documentation is pretty sparse. Richie Cotton and I just got funding from the RConsortium to expand this considerably. See here for a draft of our package aimed at making it easier to manage translations in packages. I'd be happy to collaborate, hear ideas, get input, and start coding on this more, if there's interest.

[seankross]

@leeper awesome! I'll take a look.