I use a custom translate function from a singleton object in qml with the following syntax in the main.qml:

import Translator 1.0

Text {

   text: CustomTranslator.tr("xxx")

}

To generate TS files I do :
 

lupdate main.qml -ts fr.ts -tr-function-alias qsTr=CustomTranslator.tr

Unfortunately the parser do not catch any translations.

The dotted notation seems to be an issue

Output is:

Updating 'fr.ts'...
    Found 0 source text(s) (0 new and 0 already existing)