Qt Linguist QM file not being loaded

I am using QT Linguist 5.13.2 on Windows 10.

The project has a number of translation files which all work, apart from the one for Italian.

Here is an snippet of the relevant code where the option is mapped to a qm file:

void Stg::initTranslators()
{
    _translatorEn = new QTranslator(this);
    _translatorPl = new QTranslator(this);
    _translatorFr = new QTranslator(this);
    _translatorDe = new QTranslator(this);
    _translatorNl = new QTranslator(this);
    _translatorEs = new QTranslator(this);
    _translatorIt = new QTranslator(this);
    _translatorPt = new QTranslator(this);
    _translatorAr = new QTranslator(this);
    _translatorZh = new QTranslator(this);

    _translatorEn->load(QStringLiteral(":/translation/translation/trn_en.qm"));
    _translatorPl->load(QStringLiteral(":/translation/translation/trn_pl.qm"));
    _translatorFr->load(QStringLiteral(":/translation/translation/trn_fr.qm"));
    _translatorDe->load(QStringLiteral(":/translation/translation/trn_de.qm"));
    _translatorNl->load(QStringLiteral(":/translation/translation/trn_nl.qm"));
    _translatorEs->load(QStringLiteral(":/translation/translation/trn_es.qm"));
    _translatorIt->load(QStringLiteral(":/translation/translation/trn_it.qm"));  // Italian
    _translatorPt->load(QStringLiteral(":/translation/translation/trn_pt.qm"));
    _translatorAr->load(QStringLiteral(":/translation/translation/trn_ar.qm"));
    _translatorZh->load(QStringLiteral(":/translation/translation/trn_zh.qm"));
}

In the code when the language is selected this code is executed to set the language:

    switch (_appLanguage) {
    case LANG_EN : { qApp->installTranslator(_translatorEn); } break;
    case LANG_PL : { qApp->installTranslator(_translatorPl); } break;
    case LANG_FR : { qApp->installTranslator(_translatorFr); } break;
    case LANG_DE : { qApp->installTranslator(_translatorDe); } break;
    case LANG_NL : { qApp->installTranslator(_translatorNl); } break;
    case LANG_ES : { qApp->installTranslator(_translatorEs); } break;
    case LANG_IT : { qApp->installTranslator(_translatorIt); } break;  // Italian
    case LANG_PT : { qApp->installTranslator(_translatorPt); } break;
    case LANG_AR : { qApp->installTranslator(_translatorAr); } break;
    case LANG_ZH : { qApp->installTranslator(_translatorZh); } break;
    default : { } break;
    }

All languages switch correctly, apart from Italian.

To determine if the issue is the translation file, or the switching code, I change the mapping to Arabic for the Italian selection:

    _translatorIt->load(QStringLiteral(":/translation/translation/trn_ar.qm"));  // Italian

With this the language settings do switch to Arabic when selecting Italian, which suggest the issue is in the trn_it.ts and/or the generated trn_it.qm.

When I load the trn_it.ts file into Qt Linguist it reports no errors, and the trn_it.qm file generated (via File->Release) is about the right size (as the other language qm files).

Doing a diff between the trn_it.ts and trn_de.ts files reveals the only differences are the expected <translation> elements. Everything else is the same.

Here is a snippet:

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE TS>
<TS version="2.1" language="en_US">
<context>
    <name>AboutDialog</name>
    <message>
        <location filename="ui/aboutdialog.cpp" line="90"/>
        <location filename="ui/aboutdialog.cpp" line="98"/>
        <source>Unregistered</source>
        <translation>Non registrato</translation>
    </message>

I'm at a loss to explain this, and how to debug this further.

After much trial and error, I found the reason for the Italian translation not working was because the trn_it.qm file (which was new) had not been added as a resource (eg via Qt Creator) for the project.

Once this was done, clean and rebuild did the trick.