i18n model doesn't work properly

Evening, experts,

I have a code that checks a response from a server and shows message box according to the information received. I have these messages in 2 languages (user selects a language during login). Here is example:

if(sResponse == 'IDfail'){    sap.m.MessageBox.alert    ("{i18nResourceModel>idnotnine}",         {icon: sap.m.MessageBox.Icon.ERROR,        title: "{i18nResourceModel>error}"}    );
}

Here is i18n model declaration (it is declared before I use the model, of course):

var oResourceModel = new sap.ui.model.resource.ResourceModel    ({bundleUrl: "i18n/i18n.properties", bundleLocale: "en"});
sap.ui.getCore().setModel(oResourceModel, "i18nResourceModel");

I have 2 .properties files: i18n.properties (english) and i18n_iw.properties (hebrew).

The strange thing is that the title of the message box is displayed correctly, but instead of the message itself I see text: i18nResourceModel>idnotnine.

It worked fine before and I can't figure out what happened.

What may be causing this issue and how do I fix it?

Thank you.