[libcalamares] Translatable config strings use tr()-infrastructure

- Allow TranslatedString to get a context parameter; if it has
  one, it will try to use the regular tr()-infrastructure
  **as fallback** for the translations from the config file itself.
- This makes it possible to offer -- and translate -- some "standard"
  phrases in the module, while allowing the config file the knob
  to change strings. Using one of the standard strings gets translations
  for "free", while introducing something entirely new means sourcing
  translations for it as well.

src/libcalamares/locale/TranslatableConfiguration.cpp

@@ -23,6 +23,7 @@
 #include "utils/Logger.h"
 #include "utils/Variant.h"
 
+#include <QCoreApplication>
 #include <QRegularExpression>
 #include <QRegularExpressionMatch>
 
@@ -34,7 +35,9 @@ TranslatedString::TranslatedString( const QString& string )
 {
     m_strings[ QString() ] = string;
 }
-TranslatedString::TranslatedString( const QVariantMap& map, const QString& key )
+
+TranslatedString::TranslatedString( const QVariantMap& map, const QString& key, const char* context )
+    : m_context( context )
 {
     // Get the un-decorated value for the key
     QString value = CalamaresUtils::getString( map, key );
@@ -99,7 +102,17 @@ TranslatedString::get( const QLocale& locale ) const
         }
     }
 
-    return m_strings[ QString() ];
+    // If we're given a context to work with, also try the same string in
+    // the regular translation framework.
+    const QString& s = m_strings[ QString() ];
+    if ( m_context )
+    {
+        return QCoreApplication::translate( m_context, s.toLatin1().constData() );
+    }
+    else
+    {
+        return s;
+    }
 }
 
 

src/libcalamares/locale/TranslatableConfiguration.h

@@ -40,7 +40,7 @@ class DLLEXPORT TranslatedString
 public:
     /** @brief Get all the translations connected to @p key
      */
-    TranslatedString( const QVariantMap& map, const QString& key );
+    TranslatedString( const QVariantMap& map, const QString& key, const char* context = nullptr );
     /** @brief Not-actually-translated string.
      */
     TranslatedString( const QString& string );
@@ -73,6 +73,7 @@ public:
 private:
     // Maps locale name to human-readable string, "" is English
     QMap< QString, QString > m_strings;
+    const char* m_context = nullptr;
 };
 }  // namespace Locale
 }  // namespace CalamaresUtils