loctool have plugin for QML app's localization. ilib-loctool-webos-qml and ilb-loctool-webos-ts-resource It's implemented for webOS QML application, but it could be used for general QML application too.

1) Extract localizable Strings

ilib-loctool-webos-qml plugin takes qml and js type files and extract localizable strings.
If you use the following methods and macros, the text inside it will be extracted as a localizable string.

Text { text: qsTr("hello") }
Text { text: qsTranslate("CustomContext", "hello") }

Item {
    property string greeting: QT_TR_NOOP("hello")

    Text { text: qsTr(greeting) }
}

2) Prepre XLIFF files

Prepare multi-language XLIFF files with translation.
With loctool parameter or through a config file, It can set xliff files location.

// a) loctool option
 -x or --xliffs
  Specify the dir where the xliffs files live. Default: "."

// b) set in project.json config file
...
"settings": {
    "xliffsDir": "./xliffs",
... 

3) Write config file for loctool

Make sure resourceDirs, resourceFileType and plugin are written correctly in project.json file.

i.e) project.json

...
"resourceDirs": {
    "ts":"resources"
},
"resourceFileTypes": {
    "ts":"ilib-loctool-webos-ts-resource"
},
"plugins": [
    "ilib-loctool-webos-qml",
    "ilib-loctool-webos-appinfo-json"
],
...

4) Run the loctool - Generate localization data (*.ts file)

ilib-loctool-webos-ts plugin localization data as TS file format.
TS file format used by QT Linguist. Here's simple ts file form.

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE TS>
<TS version="2.1" language="ko-KR" sourcelanguage="en-KR">
  <context>
    <name>LocalizationToolTest</name>
    <message>
      <location filename="LocalizationToolTest.qml"></location>
      <source>Hello</source>
      <translation>안녕하세요</translation>
    </message>
  </context>
</TS>

5) Generate QML file format (*.qm file)

With ts files from loctool running, Developer need to run lrelease to get QML file format. It's compact binary format that is used by the localized application.
The lrelease command line tool produces QM files out of TS files. The QM file format is a compact binary format that is used by the localized application. It provides extremely fast lookups for translations. The TS files lrelease processes can be specified at the command line, or given indirectly by a Qt .pro project file.

lrelease can be also be run without specifying a .pro file:

lrelease.exe main_en.ts languages\main_fr.ts

Reference

• https://doc.qt.io/qt-6/qml-qtqml-qt.html
• https://doc.qt.io/qt-6/qtglobal.html
• https://doc.qt.io/qt-5/linguist-manager.html