Allow grammatically correct localisation of the RelativeTime plugin to fusional languages

[prantlf]

• Redefine the locale object structure to separate expressions for duration, future and past. Allow the proper declension of the noun coming after the numeral.
• Automatically convert the old locale object structure to the new one during the first call to a method of the RelativeTime plugin.

Redefining the locale object structure from the old one:

  relativeTime: {
    future: 'in %s',
    past: '%s ago',
    s: 'a few seconds',
    ...
    yy: '%d years'
  }

to the new one solves the problem 1 from #302:

  relativeTime: {
    duration: {
      s: 'a few seconds',
      ...
      yy: '%d years'
    },
    future: {
      s: 'in a few seconds',
      ...
      yy: 'in %d years'
    },
    past: {
      s: 'a few seconds ago',
      ...
      yy: '%d years ago'
    }
  }

Adding second expressions with three-letter keys for numerals greater or equal to 5 solves the problem 2 from #302:

    duration: {
      s: 'a few seconds',
      m: 'a minute',
      mm: '%d minutes',
      mmm: '%d minutes',
      ...
    },

My Czech localisation is an example how to use the new locale structure to support grammatically correct formatting.

[codecov-io]

Codecov Report

Merging #304 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #304    +/-   ##
======================================
  Coverage     100%   100%            
======================================
  Files          32     44    +12     
  Lines         386    488   +102     
  Branches       53     65    +12     
======================================
+ Hits          386    488   +102

Impacted Files	Coverage Δ
src/locale/ru.js	100% <ø> (ø)	⬆️
src/plugin/relativeTime/index.js	100% <100%> (ø)	⬆️
src/locale/cs.js	100% <100%> (ø)
src/locale/es.js	100% <0%> (ø)	⬆️
src/locale/de.js	100% <0%> (ø)	⬆️
src/locale/fr.js	100% <0%> (ø)	⬆️
src/locale/it.js	100% <0%> (ø)	⬆️
src/locale/ja.js	100% <0%> (ø)	⬆️
src/index.js	100% <0%> (ø)	⬆️
... and 12 more

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[prantlf]

I extended the localization format to cover all possible languages. The simple adding of a new string key was not enough. Even the common languages were not covered well with the three plural forms and the single rule for them, as @leovp pointed out.

Newly, the plural rule (a number or a function) has to be specified and the plural forms are specified as an array of strings, which the plural rule is an index to.

  relativeTime: {
    // Slavic (Slovak, Czech), 3 plural forms for 1, 2-4, 5-
    pluralRule: 8,
    duration: {
      s: 'několik sekund',
      m: 'minuta',
      mm: ['%d minuta', '%d minuty', '%d minut'],
      h: 'hodina',
      hh: ['%d hodina', '%d hodiny', '%d hodin'],
      d: 'den',
      dd: ['%d den', '%d dny', '%d dní'],
      M: 'měsíc',
      MM: ['%d měsíc', '%d měsíce', '%d měsícú'],
      y: 'rok',
      yy: ['%d rok', '%d roky', '%d let']
    },
    future: {
      s: 'za několik sekund',
      m: 'za minutu',
      mm: ['za %d minutu', 'za %d minuty', 'za %d minut'],
      h: 'za hodinu',
      hh: ['za %d hodinu', 'za %d hodiny', 'za %d hodin'],
      d: 'zítra',
      dd: ['za %d den', 'za %d dny', 'za %d dní'],
      M: 'za měsíc',
      MM: ['za %d měsíc', 'za %d měsíce', 'za %d měsícú'],
      y: 'za rok',
      yy: ['za %d rok', 'za %d roky', 'za %d let']
    },
    past: {
      s: 'před několika sekundami',
      m: 'před minutou',
      mm: ['před %d minutou', 'před %d minutami', 'před %d minutami'],
      h: 'před hodinou',
      hh: ['před %d hodinou', 'před %d hodinami', 'před %d hodinami'],
      d: 'včera',
      dd: ['před %d dnem', 'před %d dny', 'před %d dny'],
      M: 'před měsícem',
      MM: ['před %d měsícem', 'před %d měsíci', 'před %d měsíci'],
      y: 'vloni',
      yy: ['před %d rokem', 'před %d roky', 'před %d lety']
    }
  }

The plural rule can be either a number from src/plugin/relativeTime/pluralRules.js (an index in the array) or a function.

    pluralRule: 8

    pluralRule: n => n === 1 ? 0 : n >= 2 && n <= 4 ? 1 : 2

The plural forms are an array of strings, where the first one is for 1 item (singular, or 21, 31 and other numbers, depending on the language) and the others are supposed to match the index returned by the plural rule function. If there is only a single special case how to handle zero, this should be the last one (with the highest index). Singulars for the value 1 are special, because they usually have no number in the text.

I upgrade earlier locale format versions to retain the compatibility.

[kmisachenka]

Hi! There is any progress for this issue?

[iamkun]

I think RelativeTime plugin has better support for fusional languages now.
I'll close this PR since it's been a while since it's been opened. Feel free to reopen if you have updates on this