qt: Use only Qt translation primitives in GUI code

Use `QObject::tr`, `QT_TR_NOOP`, and `QCoreApplication::translate` as
appropriate instead of using `_()` which doesn't get picked up.

Author: laanwj

src/qt/bitcoin.cpp

@@ -154,10 +154,11 @@ static bool InitSettings()
 
     std::vector<std::string> errors;
     if (!gArgs.ReadSettingsFile(&errors)) {
-        bilingual_str error = _("Settings file could not be read");
-        InitError(Untranslated(strprintf("%s:\n%s\n", error.original, MakeUnorderedList(errors))));
+        std::string error = QT_TRANSLATE_NOOP("bitcoin-core", "Settings file could not be read");
+        std::string error_translated = QCoreApplication::translate("bitcoin-core", error.c_str()).toStdString();
+        InitError(Untranslated(strprintf("%s:\n%s\n", error, MakeUnorderedList(errors))));
 
-        QMessageBox messagebox(QMessageBox::Critical, PACKAGE_NAME, QString::fromStdString(strprintf("%s.", error.translated)), QMessageBox::Reset | QMessageBox::Abort);
+        QMessageBox messagebox(QMessageBox::Critical, PACKAGE_NAME, QString::fromStdString(strprintf("%s.", error_translated)), QMessageBox::Reset | QMessageBox::Abort);
         /*: Explanatory text shown on startup when the settings file cannot be read.
             Prompts user to make a choice between resetting or aborting. */
         messagebox.setInformativeText(QObject::tr("Do you want to reset settings to default values, or to abort without making changes?"));
@@ -176,10 +177,11 @@ static bool InitSettings()
 
     errors.clear();
     if (!gArgs.WriteSettingsFile(&errors)) {
-        bilingual_str error = _("Settings file could not be written");
-        InitError(Untranslated(strprintf("%s:\n%s\n", error.original, MakeUnorderedList(errors))));
+        std::string error = QT_TRANSLATE_NOOP("bitcoin-core", "Settings file could not be written");
+        std::string error_translated = QCoreApplication::translate("bitcoin-core", error.c_str()).toStdString();
+        InitError(Untranslated(strprintf("%s:\n%s\n", error, MakeUnorderedList(errors))));
 
-        QMessageBox messagebox(QMessageBox::Critical, PACKAGE_NAME, QString::fromStdString(strprintf("%s.", error.translated)), QMessageBox::Ok);
+        QMessageBox messagebox(QMessageBox::Critical, PACKAGE_NAME, QString::fromStdString(strprintf("%s.", error_translated)), QMessageBox::Ok);
         /*: Explanatory text shown on startup when the settings file could not be written.
             Prompts user to check that we have the ability to write to the file.
             Explains that the user has the option of running without a settings file.*/

src/qt/splashscreen.cpp

@@ -184,8 +184,8 @@ static void InitMessage(SplashScreen *splash, const std::string &message)
 static void ShowProgress(SplashScreen *splash, const std::string &title, int nProgress, bool resume_possible)
 {
     InitMessage(splash, title + std::string("\n") +
-            (resume_possible ? _("(press q to shutdown and continue later)").translated
-                                : _("press q to shutdown").translated) +
+            (resume_possible ? SplashScreen::tr("(press q to shutdown and continue later)").toStdString()
+                                : SplashScreen::tr("press q to shutdown").toStdString()) +
             strprintf("\n%d", nProgress) + "%");
 }