The XTB format is a format for storing localized data, unlike the XMB format, which is used to to generate and translate the original translation.

The XTB format is an xml file with a list of key-value pairs without any deeper structure. Translations are placed inside the <translationbundle> tag in which the id attribute describes the term name and the content describes the translation.

Important

Angular's XMB translation generation generates xmb source language files, but uses xtb translation files (XML Translation Bundle: XTB).

Documentation

Official Angular i18n documentation
More about the XMB format