[e4-dev] Set up of my translation scene

[Jürgen Kropf <kropf@xxxxxxxxxxxxxxxxxxxx>]

Hi Tom,
I write this in response to your recent proposal to translation.

Albeit not (yet) using e4, we employ an approach very similar to yours 
which might be interesting to you.
(Indeed, even the names of our interfaces are identical to yours :))

We have an ITranslationService which obtains ITranslationProviders 
declared by extensions.
The actual translation is performed by an ITranslator instance which is 
obtained by the ITranslationProvider. The principal method called on 
ITranslator is getString(String key), which returns the translation for 
the given key. Some other methods, e.g. getString(String key, Object ... 
arg) or getString(String key, Locale locale) are provided too.

The ITranslationProviders follow a chain of responsibility pattern and 
one of them is selected by the ITranslationService by using the first 
one returning a non-null ITranslator for a given locale and some context 
information, which is typically a Class or Package. The locale is 
optional and substituted by the system default locale if missing.

Additionally, an integer priority value is used to obtain some ordering 
of the ITranslationProviders.

We pre-define a ResourceBundleTranslator which uses the standard 
translation using .properties files and, as the last resort, a 
KeyReturningTranslator, which has lowest priority and always returns a 
ITranslator which just returns the given key. This provider is reached 
on falling through the responsibility chain without finding a real 
translator. (Alternatively, one might employ an 
'ExceptionThrowingTranslator' to handle this case.)

In our applications, we further use a custom ITranslationProvider which 
is based on database lookup, and sometimes an ITranslationProvider which 
is based on com.google.api.translate.Translate, i.e. uses Google for the 
translation. Of course, the latter one is in no way perfect, but quite 
handsome for easily providing translations in exotic languages.

The priority sequence for our ITranslationProviders is (from high to low):
Database,
ResourceBundle ,
Google,
KeyReturning


In the following code example I have included a simple mechanism we use 
to dynamically react on locale changes. These are managed by the 
ITranslationService and notifications are fired for interested listeners.

public class SomeClass implements ILocaleChangeListener {

   private ITranslator Messages; // we name it 'Messages', so we can 
use the 'Externalize Strings...' feature of Eclipse
   private String translated;


   public SomeClass() {
       ITranslationService translationService = (ITranslationService) 
PlatformUI.getWorkbench().getService(ITranslationService.class);
       translationService.addLocaleChangeListener(this);  // we want be 
informed on locale changes
       Messages = translationService.getTranslator(SomeClass.class); // 
get a translator for the current default locale

       //...

       // looks identical to the .properties translation, but the 
translation might indeed be performed by database lookup etc
       // this is completely transparent to the application
       translated = Messages.getString("SomeClass.someKeyToTranslate"); 
//$NON-NLS-1$
       // ...
   }


   @Override
   // called after the locale has been changed by the ITranslationService
   public void localeChanged(ITranslationService service, Locale 
oldLocale, Locale newLocale) {

        // we just obtain an ITranslator appropriate for the new situation
        //  newLocale could be omitted, because ITranslationService 
sets the system default locale
        Messages = translationService.getTranslator(SomeClass.class, 
newLocale);

        // perform some translation for the new Locale
        translated = 
Messages.getString("SomeClass.someKeyToTranslate"); //$NON-NLS-1$
        // ...
   }
}

Please excuse me for posting this stuff to the e4 development list 
without having a clear dependency to e4,
but the similarities with your proposal seemed so, that this might be 
justified.

A happy new year

Juergen