[errai-dev] ErraiUI and i18n

[Jonathan Fuerth]

Hi all,

Eric Wittmann has volunteered to implement proof-of-concept internationalization features in ErraiUI. To get things going, he asked me to sum up the conversation we had on a GitHub pull request[1]. Here's my summary, as I understand it.

Goals:
 * Must not compromise on 'designer templates:' the template must be 100% valid HTML5 and render properly in a browser as-is.
 * Aim for least possible amount of boilerplate in the common case: if I18N is invisible on 80% of the fields it affects (both Java side and HTML side) then we're winning.
 * At compile time, we'll generate reports on the state of each translation: for each language, which translations are missing and which are orphaned? If this is summarized numerically in a .properties file, it's trivially easy to track in Jenkins with the Plot plugin[2].
 * Must be able to substitute different images based on user's language
 * Ability to translate both text within an element as well as attribute values in tags
 * Should accommodate simple HTML markup within messages (eg. anything SafeHtml would allow)
 * Support user selection of language independent of what the accept-language header says

Non-Goals:
 * We're not attempting to define something that works outside of Errai UI templates and @Templated classes
 * We're not considering the ability to define structurally different page layouts based on locale (Android can do this with its resources system)
 * We're not talking about reacting to anything except the user's language preference (again, Android's resource system supports varying resources based on screen size, resolution, language, country, and lots more besides)

Open Questions:
 * Should we use GWT's message resource file format?
 * When/if we specify a key, should it be in the template file (eg, as a data-i18n="message.key" attrbute) or in the Java class (as an @I18n("message.key") annotation on the @DataField)? ewittmann originally proposed the attribute-in-template approach, and okrasz and w0mbat expressed a preference for that too.
 * How will we handle interpolation into messages (for example Hello {name}. Pleased to meet you!)? Most importantly, where do the values come from?
 * (How) do we handle special numeric formatting like $0.00 in the USA vs. 0,00€ in Europe? It seems we may need a mechanism to call out to GWT's number formatting classes


Based on all that, here's a strawman proposal to get us started (lifted from Eric's comment):

Java:

@Templated
public class MyPage extends Composite {
  
  @Inject @DataField("field1")
  private Label contentBecomesKey;
   
  @Inject @DataField("field2") @I18n("mypage.description")
  private Label keySpecifiedInAnnotation;
   
  @Inject @DataField("field3") @I18n(value="mypage.input", attributes={"placeholder", "title"})
  private Text inputBoxWithTranslatedTooltipAndPlaceholder;

  // I don't think this will actually work well. It's just here for the sake of argument.
  @I18nParams
  private Map<String, SafeHtml> messageKeys;
}

Template:

<div data-field="templateId">
  <div data-field="field1">MyHeader</div>
  <div data-field="field2">This is a lengthy description that I don't want becoming an i18n key.</div>
  <input data-field="field3" type="text" name="field3" placeholder="Enter a value here" title="Use this data entry field to enter a valid value..." />
  <div>Innocent Bystander</div>
  <div data-field="field3">{name}, you owe {amountOwing}.</div>
</div>

Bundle for Piglatin translation:

MyHeader=yHeaderMay
mypage.description=Lorem ipsum dolor sit amet, consectetur adipiscing elit.
mypage.input.placeholder=Value here, you must enter
mypage.input.title=This data entry field, use you must...
Innocent\ Bystander=Innocentay Ystanderbay

So, thoughts?

-Jonathan

[1]: https://github.com/errai/errai/pull/24
[2]: https://wiki.jenkins-ci.org/display/JENKINS/Plot+Plugin
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