https://github.com/qt/qtvirtualkeyboard/tree/dev/src/virtualkeyboard/3rdparty shows that there are 6 libraries bundled with the Virtual Keyboard.

With the exception of hunspell, all the others are used when certain translations are used, regardless if they are found in the system. Even worse, the third party components are built statically.

For Linux distributions, and in the interest of reproducible builds, 3rd party bundled libs should be used only if the system equivalents cannot be found in the system doing the build. Also, if a distribution does not allow bundling, that would mean actually disabling translations in the package offered to users.

As desktop environments like KDE's Plasma are starting to use the Virtual Keyboard (for example in absence of a physical keyboard) and asked distributions to include it, this is an important requirement.