[JSI18N] Explicit lang in request and deactivate cache header declaration.
[JSI18N] Explicit lang in request and deactivate cache header declaration.

The `jsi18n` depends of the session current language.

By changing the url from `/jsi18n` to `/lang/jsi18n` we explicit the
current language used (as for other pages) and we can now cache it
in nginx.

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