Somewhere after receiving the data:
const popupString = popupData.template.replace(
/{{\s?([^{}\s]*)\s?}}/g,
(substring, parsedKey) => {
const replacer = popupData.data[parsedKey];
return typeof replacer !== 'undefined' ? replacer : substring;
}
);
It should equal the <b>world</b> says Hello
in your example.
Please note that this code comes from robisim74s angular -l10n (MIT license).