Wrong translation is loaded when translation is not vailable

[Wiktor Walc]

When opening a plugin with its own language files, and the selected language is not available, the first available translation is loaded.

Which means that the same instance is using: user language (e.g. Italian) AND Afrikaans, Arabic, Bulgarian etc.

To reproduce, take the uicolor plugin, remove "it" from "lang" property, configure the Italian language to be the default one and launch samples/uicolor.html

Happens both, in source and release version.

[Garry Yao]

Opened dev branch t/9688 for review.

Language probing feature is now added to plugin language loading, although plugin language loading requires further simplification I'd not propose them in this patch.

[Piotrek Koszuliński]

It'd be unwise to masterise today branch with these stats:

 core/editor.js                |   17 ++++++++---------
 core/lang.js                  |   35 ++++++++++++++++++++++-------------
 core/tools.js                 |   16 ++++++++++++++++
 plugins/a11yhelp/plugin.js    |    8 ++++----
 plugins/specialchar/plugin.js |    9 ++++-----

If possible, simpler fix should be proposed.

[Piotrek Koszuliński]

Pushed t/9688b with very simple fix. If there's no translation for current editor's language, it tries to load english and if that fails, first one.

[Garry Yao]

t/9688b is OK...but it doesn't help that much on the issue:

1. "En" doesn't have to be the default language configured by user.
2. There's no fix for the language entries of plugin dialog.
3. There's no fallback for local languages with non-local version. (zh-cn -> zh)

[Garry Yao]

I hope a review can be still taken on t/9688, in fact it's not actually a big change, it's not more than a signature change.

[Frederico Caldeira Knabben]

Indeed, t/9688 is not acceptable at this stage.

[Frederico Caldeira Knabben]

t/9688b is good, but in fact misses the fallback feature. I've just pushed this.

[Frederico Caldeira Knabben]

Fixed with ​git:e096626.