i18n: make sure 'en' in Accept-Language is recognized as having 100% coverage - i18n.lang is for source language https://github.com/cdent/paste/blob/3.2.3/paste/wsgiwrappers.py#L89 describes how paste solved the problem. TG solves the same problem (with less explanation) in https://github.com/TurboGears/tg2/blob/tg2.4.2/tg/request_local.py#L36 with fallback language specified in i18n.lang . Thus, clarify the use of i18n.lang (refining f2f7a8c1281e and 8931078f70db) and set 'en' as default value on app startup. TurboGears requires an (empty) translation for the source language which is default for i18n.lang . The empty .mo for en is created as the 4 magic .mo bytes followed by lengths of 0: printf '\x95\x04\x12\xde\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0' > kallithea/i18n/en/LC_MESSAGES/kallithea.mo Based on report and analysis by Wolfgang Scherer. Also discussed upstream on https://github.com/TurboGears/tg2/pull/115 .