Comment 2 for bug 1798535

I think I found the reason here. Looking at https://launchpad.net/ubuntu/+source/language-pack-hy, the last Ubuntu release to include the Armenian language pack was Ubuntu 14.04. Based on https://launchpad.net/ubuntu/+source/language-pack-hy/+publishinghistory it looks like the language pack was removed for having less that 5% translations.

Currently around 3% of the text in Ubuntu is translated to Armenian https://translations.launchpad.net/ubuntu/. I suppose if the translation team (https://launchpad.net/~ubuntu-l10n-hy) manages to translate a larger part, then the language would be re-included.

(I've also marked this as affecting Ubuntu-translations, so that someone can check I'm interpreting the removal correctly.)