Plugin Directory: No call to improve an existing translation

[SergeyBiryukov]

Before the redesign, each plugin had a "Translations" widget in the sidebar with a list of languages the plugin is translated to and a nice green Translate [plugin name] button (see the screenshot).

In the new design, the list of languages is hidden under "Development" tab. The locale banner at the top is supposed to be more prominent, but it doesn't cover all use cases the old widget did:

• If the plugin doesn't have a language pack for a particular locale yet, a notice is displayed: This plugin is not available in [language name] yet. <a href="%s">Help translate it!</a>. So far so good.
• If the plugin already has a language pack, there's another notice: This plugin is also available in [language name]. The link leads to the plugin page on the corresponding Rosetta site, which might seem like a good idea, but there's no longer a call to improve the translation.

It's still possible to go to the translation project from the plugin page, but the way to do that is a bit convoluted and isn't obvious for a translator at all. There's a good chance they won't find the link unless they already know where to look:

1. Click "Development" tab.
2. Click "Read more" link.
3. Click "Translate [plugin name] into your language."

Suggestion: Add a call to improve the translation to the second notice: This plugin is also available in [language name]. <a href="%s">Help improve the translation!</a>.

[SergeyBiryukov]

Suggestion: Add a call to improve the translation to the second notice: This plugin is also available in [language name]. <a href="%s">Help improve the translation!</a>.

Note: This doesn't cover the case when a plugin is viewed in a localized directory (as there's no locale banner in that case), but it still seems like a good first step.

[tellyworth]

In 5717:

Plugin directory: Add "help improve this translation" links to the locale banner. Props @SergeyBiryukov.

Fixes #2921

[SergeyBiryukov]

In 5983:

Plugin Directory: After [5717], update strings for the POT file as well.

See #2921.

[SergeyBiryukov]

In 6121:

Plugin Directory: After [5717], update strings in Locale_Banner::translate() as well.

See #2921.