i18n_subsites: described concept of jinja2.ext.i18n support
i18n_subsites: only load translation for current DEFAULT_LANG

others would not be used
i18n_subsites: connected install_templates_translations to generator_init
i18n_subsites: implement default localedir as descibed in documentation
i18n_subsites add docstring to install_templates_translations
i18n_subsites: apparently setting the lang for gettext.translate is enough
i18n_subsites: fallback to NullTranslations if translations cannot be found
i18n_subsites: fix syntax error
i18n_subsites: swap phase 2 and 3 to first specify domain and location