Didier Roche authored Mar 01, 2019 and Carlos Soriano Sánchez committed Jun 19, 2020

UI files needs C Gettext to be initiliazed. This one can only work from
.mo files and not from memory binary data.

Consequently, if useCgettext is set to true:
- external mode isn't impacted (mo files are on disk), apart from local
choice (see below)
- embedded mode select the correct mo data (from localization.go embedded
data) and dump it into a temporary locale directory structure with
that file content on application startup, before initializing C gettext.
This will be cleaned up on shutdown.
- dev mode is like embedded mode with an additional startup step: we
compile the corresponding po file to mo file first. This modes thus
requires `msgfmt` to be on system where people run this dev mode weeport
binary.

To ensure we are loading from the Go side the same locale than the one
gettext would choose for ui files, we are going to use the returned locale
by setlocale() instead of our algorithm.
If useCgettext is set to false, we disable the whole C determinism and
initialization for locales.