How to install lrelease for QT 5.12 when buidling snaps?

snapcraft
1

I want to build a snap using the following snapcraft.yml:

name: minitube
base: core18
version: '3.2'
summary: Flavio Toldini's minitube youtube player.
description: |
  "Watch YouTube videos in a new way: you type a keyword, Minitube gives you an endless video stream.
  Minitube is not about cloning the YouTube website, it aims to create a new TV-like experience."

grade: devel
confinement: devmode

apps:
  minitube:
    command: bin/desktop-launch  bin/ninitube
    plugs: [x11, network, home]
    environment:
      LD_LIBRARY_PATH: $LD_LIBRARY_PATH:$SNAP/usr/local/lib

parts:

  libmpv:
    source: https://github.com/mpv-player/mpv-build.git
    plugin: nil
    override-build : |
     pip3 install youtube-dl
     echo --enable-libx264 >> ffmpeg_options
     echo --enable-libmp3lame >> ffmpeg_options
     echo --enable-libfdk-aac >> ffmpeg_options
     echo --enable-nonfree >> ffmpeg_options
     echo --enable-libmpv-shared > mpv_options
     ./use-mpv-custom v0.29.1
     ./update
     ./rebuild -j4
     sudo ./install
    build-packages:
      - dh-autoreconf
      - build-essential
      - libfreetype6-dev
      - libfribidi-dev 
      - libfontconfig1-dev 
      - yasm 
      - libmp3lame-dev 
      - libx264-dev 
      - libfdk-aac-dev 
      - libpulse-dev
      - python3
      - python3-pip

  qt5:
    source: https://github.com/ubuntu/snapcraft-desktop-helpers.git
    source-subdir: qt
    plugin: make
    make-parameters: ["FLAVOR=qt5"]
    build-packages:
      - qtbase5-dev
      - dpkg-dev
    stage-packages:
      - libxkbcommon0
      - ttf-ubuntu-font-family
      - dmz-cursor-theme
      - light-themes
      - adwaita-icon-theme
      - gnome-themes-standard
      - shared-mime-info
      - libqt5gui5
      - libgdk-pixbuf2.0-0
      - libqt5svg5 # for loading icon themes which are svg
      - try: [appmenu-qt5] # not available on core18
      - locales-all

  app:
    source: .
    plugin: qmake
    options: 
      - "DEFINES += APP_GOOGLE_API_KEY=${GOOGLE_API_KEY}"
    build-snaps:
      - kde-frameworks-5-core18-sdk
      - kde-frameworks-5-core18
    override-build: |
      export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$SNAP/usr/local/lib
      snapcraftctl build
    after:
      - qt5
      - libmpv

But once I build the following app part I get the following response:

qmake LIBS+="-L/home/pc_magas/minitube/stage/lib" LIBS+="-L/home/pc_magas/minitube/stage/usr/lib" LIBS+="-L/home/pc_magas/minitube/stage/lib/x86_64-linux-gnu" LIBS+="-L/home/pc_magas/minitube/stage/usr/lib/x86_64-linux-gnu" INCLUDEPATH+="/home/pc_magas/minitube/stage/usr/include" DEFINES += APP_GOOGLE_API_KEY=${GOOGLE_API_KEY}
Project MESSAGE: Building Minitube 3.2
Project MESSAGE: Qt 5.12.0 in /opt/qt512
make -j2
/opt/qt512/bin/lrelease locale/ar.ts -qm build/target/locale/ar.qm
make: /opt/qt512/bin/lrelease: Command not found
/opt/qt512/bin/lrelease locale/ast.ts -qm build/target/locale/ast.qm
make: /opt/qt512/bin/lrelease: Command not found
Makefile:904: recipe for target 'build/target/locale/ar.qm' failed
make: *** [build/target/locale/ar.qm] Error 127
make: *** Waiting for unfinished jobs....
Makefile:907: recipe for target 'build/target/locale/ast.qm' failed
make: *** [build/target/locale/ast.qm] Error 127
Failed to run 'make -j2' for 'app': Exited with code 2.
Verify that the part is using the correct parameters and try again.

So how I can install the lrelease for QT 5.12? Because the developer of the software that I snap sometimes may use the latest and greatest version of Qt without any warning I want to be able to build from source.