Yeah, seems to me it's an Invision problem. I run both IPB (older 4.x version) and Xenforo and if I use the selection box to choose a language, I get all languages, even African and Chinese and whatever. And also Italian.
Even if I choose "create new -> upload" on the selection box I can even choose various arabic languages, Italian, African, a whole list.
Is that "translations" option something new of IPB or is it an addon to import translations? Because I always had to use the pencil image and then select language and create new.
I had no issue installing a Dutch language, while the locale was en_US.UTF-8 so there must be something else wrong imho. I don't have anything in Dutch in my locale.
Seems your selection box only contains English, so that is odd. Seems like something in your installation is messed up. That is an IPB problem, not a DA problem. Or it's an OS problem.
Use this command in SSH to see which locales are supported.
localectl list-locales
However, since your locale and localectl both state the Italian language, you should be fine.
You don't have the default admin theme and it seems you have some basket selected instead of the pencil which is the normal place to start creating and/or uploading new languages. Or has this changed in the newest version? It might even be a bug i IPB or an addon which is doing things wrong.
What you could still try, instead of it_IT fill in it_IT.UTF-8 which is the correct locale. Maybe then it will go through.
However, it's certainly not a DA issue. Because the locale is part of the operating system. And for example Centos 7 is supporting most locales.
Did you show the IPB support guys the screenshot of your locale and localectl output? Because that shows Italian is supported.
