Qt Software Localizastion (and more) -- https://16bpp.net/blog/post/localizing-a-qt-app-or-anything-else-for-that-matter/

CMakeLists.1.txt

# `Linguist` is required
find_package(Qt6 COMPONENTS Linguist REQUIRED)

# ...

# Have your app specified
qt_add_executable(myapp ...

# ...

# Specify your translations
qt_add_translations(myapp
  TS_FILES
  i18n/myapp_de_DE.ts
  i18n/myapp_ja_JP.ts
)

CMakeLists.2.txt

# Specify your translations
qt_add_translations(myapp
  TS_FILES
  i18n/myapp_de_DE.ts
  i18n/myapp_ja_JP.ts
)
add_dependencies(myapp release_translations)

Messages.qml

// User facing strings
QtObject {
  // Render View
  readonly property string app_window_title:        qsTr('PSRayTracing (GUI Edition)')
  readonly property string scene_label:             qsTr('Scene:')
  readonly property string stop:                    qsTr('Stop')
  readonly property string render:                  qsTr('Render')
  readonly property string total_render_time_fmt:   qsTr('Total Render Time: %1')
  
  // ...

myapp_de_DE.ts

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE TS>
<TS version="2.1" language="de_DE">
<context>
  <name>QObject</name>
  <message>
    <source>No</source>
    <comment>denial</comment>
    <translation type="obsolete">Nein</translation>
  </message>
  <message numerus="yes">
    <location filename="main.cpp" line="36"/>
    <source>%Ln Apple(s)</source>
    <translation type="unfinished">
      <numerusform>%Ln Apfel</numerusform>
      <numerusform>%Ln Äpfel</numerusform>
    </translation>
  </message>
</context>
</TS>

qlocal_translation_forcing_main.cpp

// Find this line
const QString baseName = "myapp_" + QLocale(locale).name();

// Change it to this
const QString baseName = "myapp_" + QLocale().name();

qlocale_main.cpp

QLocale::setDefault(QLocale::German);

qstringliteral_example.1.cpp

auto lbl = new QLabel("Hi Mom!");
QString filePath = "data.csv";

qstringliteral_example.2.cpp

auto lbl = new QLabel(tr("Hi Mom!"));
QString filePath = QStringLiteral("data.csv");

qDebug() << "Doing this with qDebug() is still okay though!"

qtquickcontrols2_ja_JP.conf

[Controls]
Style=Basic

[Basic]
Font\PointSize=15

rcc.qrc

<RCC>
  <qresource prefix="/">
    <file>qtquickcontrols2.conf</file>

...

  <!-- Japanese specific resources -->
  <qresource prefix="/" lang="ja">
    <file alias="qtquickcontrols2.conf">i18n/qtquickcontrols2_ja_JP.conf</file>
  </qresource>
</RCC>

RenderSettingsForm.qml

id: fields_layout

readonly property bool _small_width:    UITheme.is_width_small(parent.width)
readonly property int column_count:     (_small_width ? 1 : 2)

// ...

columns: fields_layout.column_count

translation_installer.main.cpp

QTranslator translator;
const QStringList uiLanguages = QLocale::system().uiLanguages();
for (const QString &locale : uiLanguages) {
    const QString baseName = "myapp_" + QLocale(locale).name();
    if (translator.load(":/i18n/" + baseName)) {
        app.installTranslator(&translator);
        break;
    }
}