sourcelanguage instead of targetlanguage

it generates a general ts file instead of a file per targetlanguage

src/app/qgsprojectproperties.cpp

@@ -2218,4 +2218,10 @@ void QgsProjectProperties::onGenerateTsFileButton() const
 {
   QString l = cbtsLocale->currentData().toString();
   QgsProject::instance()->generateTsFile( l );
+  QMessageBox::information( nullptr, tr( "General TS file generated" ), tr( "TS file generated with source language %1.\n"
+                            "- open it with Qt Linguist\n"
+                            "- translate strings\n"
+                            "- save it with the postfix of the target language (eg. de)\n"
+                            "- release to get qm file including postfix (eg. aproject_de.qm)\n"
+                            "When you open it again in QGIS having set the target language (de), the project will be translated and saved with postfix (eg. aproject_de.qgs)." ).arg( l ) ) ;
 }

src/core/qgsproject.cpp

@@ -2820,7 +2820,7 @@ void QgsProject::generateTsFile( const QString &locale )
 {
   QgsTranslationContext translationContext;
   translationContext.setProject( this );
-  translationContext.setFileName( QStringLiteral( "%1/%2_%3.ts" ).arg( absolutePath(), baseName(), locale ) );
+  translationContext.setFileName( QStringLiteral( "%1/%2.ts" ).arg( absolutePath(), baseName() ) );
 
   emit QgsApplication::instance()->collectTranslatableObjects( &translationContext );
 

src/core/qgstranslationcontext.cpp

@@ -52,14 +52,11 @@ void QgsTranslationContext::registerTranslation( const QString &context, const Q
 
 void QgsTranslationContext::writeTsFile( const QString &locale )
 {
-  QgsSettings settings;
-
   //write xml
   QDomDocument doc( QStringLiteral( "TS" ) );
 
   QDomElement tsElement = doc.createElement( QStringLiteral( "TS" ) );
-  tsElement.setAttribute( QStringLiteral( "language" ), locale );
-  tsElement.setAttribute( QStringLiteral( "sourcelanguage" ), settings.value( QStringLiteral( "locale/userLocale" ), "" ).toString() );
+  tsElement.setAttribute( QStringLiteral( "sourcelanguage" ), locale );
   doc.appendChild( tsElement );
 
   for ( const TranslatableObject &translatableObject : mTranslatableObjects )

src/ui/qgsprojectpropertiesbase.ui

@@ -806,6 +806,13 @@
                   <string>Generate Project Translation File</string>
                  </property>
                  <layout class="QHBoxLayout" name="horizontalLayout_4">
+                  <item>
+                   <widget class="QLabel" name="sourceLanguageLabel">
+                    <property name="text">
+                     <string>Source language</string>
+                    </property>
+                   </widget>
+                  </item>
                   <item>
                    <widget class="QComboBox" name="cbtsLocale"/>
                   </item>
@@ -2950,6 +2957,7 @@
   <include location="../../images/images.qrc"/>
   <include location="../../images/images.qrc"/>
   <include location="../../images/images.qrc"/>
+  <include location="../../images/images.qrc"/>
  </resources>
  <connections>
   <connection>