How to change font for a particular UI (QML) when the language is either Korean or Chinese?

I have the following QML document (reduced for simplicity) -

Item {
   Label { // Label1
      text: qsTr("Label1")
   }

   Label { //Label2
      text: qsTr("Label2")
   }
}

I have a C++ class that searches for the translation QM files and call installTranslator when the application language is changed by the user. Translation is working properly.

The requirement is that I need to change the font of Label1 if the current language is Korean or Chinese but the font of Label2 should not change. If the language is not one of those two, the font for both Label1 and Label2 should be same.

Can you please tell me how can I detect if the current language is Korean or Chinese and how can we get a signal that the language has been changed when that happens?

We can solve this with qsTr().

For instance, we can introduce qsTr("western") which, by default, is "western". For Chinese, (Japanese) and Korean you can use Linguist to change qsTr("western") to, say, "cjk". Then we can use this to help switch between a default font.family versus an asian font family for just Label1 and not Label2.

   Label { // Label1
       text: qsTr("Label1")
       property TextMetrics tm: TextMetrics { }
       font.family: qsTr("western") === "western" ? tm.font.family : "some-cjk-font-family"
   }
   Label { //Label2
       text: qsTr("Label2")
   }

If you wish to apply this logic in multiple places you can refactor some properties that you can bind to:

    property string cjkCheck: qsTr("western") // "western" (default) or "cjk" (Chinese, Japanese, or Korean)
    property bool isCJK: cjkCheck !== "western"
    property TextMetrics tm: TextMetrics { }
    property string cjkFontFamily: isCJK ? "some-cjk-font-family" : tm.font.family

    Label { // Label1
        text: qsTr("Label1")
        font.family: cjkFontFamily
    }
    Label { //Label2
        text: qsTr("Label2")
    }

[EDIT]

Based on your more recent comment, another solution is you can have a LocalizedLabel, e.g.

// LocalizedLabel.qml
import QtQuick
import QtQuick.Controls
Label {
    font.family: qsTr("Arial")
}

Then, you can use the LocalizedLabel when you need it. That means, you get to default to "Arial" or choose a specific font-family and have it all managed by (1) a reusable LocalizedLabel component, (2) manage the font-family via Linguist.

    LocalizedLabel { // Label1
        text: qsTr("Label1")
    }
    Label { //Label2
        text: qsTr("Label2")
    }