QML Virtual Keyboard Add New Layout

I use qt qml 5.7 on Yocto project for raspberry pi. My project need virtual keyboard for Turkish language. QT Virtual Keyboard has no support Turkish language so i want to create my custom layout. I add my project example layout codes from here as name "myCustomLayout.qml".

And I run my virtual keyboard display function by following codes.

import QtQuick 2.5
import QtQuick.VirtualKeyboard 2.1
import QtQuick.Controls 2.0

InputPanel {
    id: inputPanel
    visible:  Qt.inputMethod.visible
    height:main.height/4
    y:main.height - height
    x:main.width/8
    width: main.width*6/8
    focus: true
}

When I run the virtual keyboard display function, the appearing keyboard was not my custom layout, it still regular English keyboard layout. How can add my custom keyboard layout in my app?

I found qtvirtualkeyboard files in yocto build path in my computer (not pi).

/build/tmp/work/cortexa7hf-neon-vfpv4-poky-linux-gnueabi/qtvirtualkeyboard/5.7.0+gitAUTOINC+626e78c966-r0/git/

I have created a new tr_TR layout files by copying en_GB file in content/layouts path. I changed my tr_TR main.qml file. I have modified virtualkeyboard.pro file like Mitch's answer by add following lines.

contains(CONFIG, lang-tr.*) {
    LAYOUT_FILES += \
        content/layouts/tr_TR/main.qml
}

Also I modified config.pri file. I changed following lines:

# Default language
!contains(CONFIG, lang-.*) {
    contains(QT_CONFIG, private_tests) { # CI or developer build, use all languages
        CONFIG += lang-all
    } else {
        CONFIG += lang-tr_TR
    }
}

# Flag for activating all languages
lang-all: CONFIG += \
#    lang-ar_AR \
#    lang-da_DK \
#    lang-de_DE \
    lang-en_GB \
#    lang-es_ES \
#    lang-fa_FA \
#    lang-fi_FI \
#    lang-fr_FR \
#    lang-hi_IN \
#    lang-it_IT \
#    lang-ja_JP \
#    lang-ko_KR \
#    lang-nb_NO \
#    lang-pl_PL \
#    lang-pt_PT \
#    lang-ru_RU \
#    lang-sv_SE \
    lang-tr_TR \
#    lang-zh_CN \
#    lang-zh_TW

I copied my changed git file to USB stick and opened my files on pi. I rebuilt qtvirtualkeyboard with:

qmake "CONFIG+=lang-all" qtvirtualkeyboard.pro
make
make install

Finally I can use my custom layout.