I took a look at your code and discovered the qsTrId() function you used.

I usually use qsTr(), where you put for example directly the english text, and then it search for translations and if there is none then fallback to this english text.

But qsTrId() is different in that it works with an id to the translated text. I can see how that could be more efficient depending on the magic they put behind the qsTr() function, but means you must somehow define a default language as a fallback.
That is not too difficult from C++ (see http://doc.qt.io/archives/qt-4.8/qtr...or.html#load-2), as the "load" function returns a boolean to tell if the locale was correctly found or not, and then loading the english could be done.
For the translations, the QLocal class provides uiLanguages (the http://doc.qt.io/archives/qt-4.8/qlo...ml#uiLanguages) function which "returns an ordered list of locale names for translation purposes in preference order". There may be a way to add the english language as a low rank choice in there...

Finally, back to the load() function from QTranslator that must be used under the hood in the QML launcher, we see the logic for finding the translations files:
So maybe renaming/symlinking/copying the english translation file as "kids-mode.ts" should be enough. I see this file is already there in your repo, but with "<translation type="unfinished"></translation>" everywhere, which I suppose would not be displayed.