I would have to point out that if you:-
cat /etc/asterisk/sip.conf|head -5
you will see why FreePBX doesn't modify that file as you suggest, the chosen "language" is specific to the used channel so should probably NOT be generalized if you want language flexibility on all endpoints and for voicemail to also work, but if you want to generalize do it in the *_custom*.conf files as appropriate.
You will also need to cover ALL your "technologies", for iax2, dahdi et al. if you use them also, FreePBX does that with more granularity within the extensions, inbound routes and trunk level bits of it's gui and downline via the generated "#include *_additional*.conf" files that asterisk will thusly use.
So things like "suoni nor צלילים" will never work but using ./sounds/{he,it} will (my first three posts) and the absence of the expected /en will likely fail (which surely was the reason for most of this thread) also in FreePBX and possibly Asterisk.
That is why I posted for both @claloano and @danielf request for clarification as to why you need /en. (my fourth post)
If you need multilanguage support on an IVR or such, than you will need a custom approach get/set'ing the ${channel(language)} variable as appropriate.
I assume @claloano has fixed his problem by appropriately creating all of ./sounds/{it,en} , so let's move on.