Detecting language - A first pass

The prep' work done to process the source file path with that first plugin was mostly done to help this second plugin. Its role will be to detect the language of each file, as well as a translation key to link translations of the same content together.

Ultimately, for a file named posts/an/ the language should be detected as French (fr) thanks to the --fr suffix. Everything preceding that suffix should be used as a the translation key. This will match it to posts/an/, its English counterpart (and to have them right next to each other).

For now, though, the French page is fr/, so let's use that for a first version of language detection.

Plugin structure

In plugins/detectLanguage.js, the structure of this second plugin will be pretty similar to the path splitting one. It loops over the files and:

module.exports = function detectLanguage() {

  return function(files, metalsmith) {
    //Grab site-wide data from the metadata
    const config = metalsmith.metadata();

    // Given all the information are in the file
    // we can iterate on the values of the object this time

      file.i18n = getLanguageInfo(file, config);

function getLanguageInfo(file, options){
  // Coming soon, really soon ;)

You might have noticed the plugin grabs some information from the metadata. Whether at the start of the path like now, or as a suffix, we'll want to limit which values are interpreted as language. "la/" doesn't write about jam in Lao, it's just a way to make a nice URL.

We can rely on the list of languages already set when creating the language switcher. We'll also add a defaultLanguage to set the default language. Oh, and let's not forget to register the plugin after the pathInfo one, in src/index.js:

// ...
const detectLanguage = require('./plugins/detectLanguage')
// ...
  i18n: {
    defaultLanguage: 'en',
    language: ['en','fr'],
// ...

Language detection

Of all the parts extracted in the pathInfo, the stem is the one of interest for this. A regular expression, built from the supported languages, will capture the language of the file and the translation key from it.

function getLanguageInfo(
  { defaultLanguage, languages } = {}
) {

  const prefix = new RegExp(`^(${languages.join('|')})/(.*)`);
  const result = prefix.exec(file.pathInfo.stem);

  // `result` will only have a value if the RegExp
  // matched anything. This way we can provide default
  // with the `else`
  if (result) {
    return {
      language: result[1],
      key: result[2]
  } else {
    return {
      language: defaultLanguage,
      key: file.pathInfo.stem

A little cleanup

With that in place, the existing fr/ automatically get its i18n.language variable set to fr, while the file should have its set to en. This means we can move on from using the language key to this new value:

We can now drop the variable from the front-matter in each of the content file (actually, the whole front-matter as it was all it content). That's that less information to add manually to each file!

It's not quite the system explained in the intro, but it's a first step. In the next article, let's finally switch to using the suffix of the file to grab the language.