Better translations for time_ago_in_words

[gravitystorm]

(Moving https://trac.openstreetmap.org/ticket/4968 here for better visibility.)

In rails there is a time_ago_in_words helper (aka distance_of_time_in_words_to_now) that we use extensively. The strings it returns are actually just the same as the distance_of_time_in_words helper, e.g. "3 years" or "about 1 hour"; that is, they doesn't come with 'ago' attached.

The logic behind the helper is fairly complex. The default translations come from the rails-i18n gem, we don't control them ourselves.

We then use these "distance_in_words" strings to create what I'll refer to as "distance_in_words_ago" strings. In English this is very easy, since every possible output of the helper can just have "ago" tacked on the end. For example

• English: "3 years" -> "3 years ago"

However, this is not the case in other languages, where to be gramatically correct, in certain cases the original "distance_in_words" needs tweaking. For example:

• Hungarian: "2 óra" -> "2 órája"
• German: "2 Tage" -> "vor 2 Tagen"

Other people identified the problem many years ago, and so since rails 3.2 the time_ago_in_words helper accepts a :scope, which allows you to pick a different i18n scope for the localisation. For example, instead of using the default en.datetime.distance_in_words from the rails-i18n gem, we could define our own distance_in_words_ago hierarchy:

en:
  datetime:
    distance_in_words_ago:
      about_x_hours:
        one: about 1 hour ago
        other: about %{count} hours ago
      about_x_months:
        one: about 1 month ago
        ...

We would then update our views, so instead of using the output from the helper in a '.ago' translation, we would set the i18n scope in the helper, and use the output directly. For example:

       <% end %>
-      ... <%= t ".ago", :time_in_words_ago => time_ago_in_words(trace.timestamp) %></span>
+      ... <%= time_ago_in_words(trace.timestamp, :scope => :'datetime.distance_in_words_ago') %></span>
       <%= link_to_if trace.inserted?, t(".map"), { :controller => "site", :action => "index", :mlat => trace.latitude, :mlon => trace.longitude, :anchor => "map=14/#{trace.latitude}/#{trace.longitude}" }, { :title => t(".view_map") } %> /

This means that our translators could translate all of the 'distance_in_words_ago' strings in a grammatically correct fashion.

Ultimately, this could also be fixed by two upstream changes. The first would be for the rails-i18n gem to include a 'distance_in_words_ago' translation hierarchy itself, which could be used by hundreds of projects beyond ours. And the secondly, the time_ago_in_words ActionView helper could then return 'distance_in_words_ago' style strings by default, which I think would be more helpful than now. But unless there's any strong opinions, I would suggest we fix this locally first.

My proposal it therefore:

• Add an en.datetime.distance_in_words_ago hierarchy to our own en.yml.
• Give the translators a few weeks opportunity to translate them.
• Update our usage of the time_ago_in_words and distance_of_time_in_words_to_now helpers to use the new hierarchy using the scope parameter.