feat: implement localization system (#716)

* lib/localization: implement localization system

Locale files are placed in lib/localization/locales/. If you add a
locale, update manifest.json with available locales.

* Exclude locales from check spelling

* tests(lib/localization): add comprehensive translations test

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(challenge/metarefresh): enable localization

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix: use simple syntax for localization in templ

Also localize CELPHASE into French according to the wishes of the
artist.

Signed-off-by: Xe Iaso <me@xeiaso.net>

* chore: spelling

Signed-off-by: Xe Iaso <me@xeiaso.net>

* chore:(js): fix forbidden patterns

Signed-off-by: Xe Iaso <me@xeiaso.net>

* chore: add goi18n to tools

Signed-off-by: Xe Iaso <me@xeiaso.net>

* test(lib/localization): dynamically determine the list of supported languages

Signed-off-by: Xe Iaso <me@xeiaso.net>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>
Co-authored-by: Xe Iaso <me@xeiaso.net>

.github/actions/spelling/excludes.txt

@@ -89,3 +89,5 @@
 ^lib/policy/config/testdata/bad/unparseable\.json$
 ignore$
 robots.txt
+^lib/localization/locales/.*\.json$
+^lib/localization/.*_test.go$

.github/actions/spelling/expect.txt

@@ -33,7 +33,7 @@ Caddyfile
 caninetools
 Cardyb
 celchecker
-CELPHASE
+celphase
 cerr
 certresolver
 cespare
@@ -42,6 +42,7 @@ cgr
 chainguard
 chall
 challengemozilla
+Chargement
 checkpath
 checkresult
 chibi
@@ -183,6 +184,7 @@ mozilla
 nbf
 netsurf
 nginx
+nicksnyder
 nobots
 NONINFRINGEMENT
 nosleep