Hi,
We bought Jira Service Desk for 3 users (starter pack) server edition, so we can test it thoroughly without time pressure. We installed server version of Service Desk and Confluence successfully. Before we can buy more user licenses we need to translate customer portal, email templates and everything that is faced towards customers. In the process of evaluation I sent a question regarding translations to you (see text below) and I received an answer what are possibilities.
This is the answer from pre-sales support:
Yes, you're correct that Slovenian is not currently available as an Atlassian Cloud language at the moment. You can see our default language options for Jira Service Desk Server on our choosing a default language page. With our Server products, you have the option to translate Jira by installing a language pack as described on our Translating Jira page and with translations from Atlassian Translations. This would be for all your Jira user screens for licensed Jira Service Desk agents. Jira Service Desk is licensed based on unique agents (users able to edit/work on requests) while customers (users submitting requests) are free.
- Requests types on the customer portal of a Jira Service Desk project are configurable based on issue types that exist in the project. You choose how to phrase the requests and statuses on your customer portal in a way that is friendly or understandable to your customers. See setting up request types for more information.
- The knowledge base functionality (provided by integrating Jira Service Desk with a product called Confluence, allows you to create Confluence Pages in a Confluence Space and link that Space to a Jira Service Desk project. The content on a Confluence Page can be in whatever language you'd like.
- For your Jira Service Desk customer portal, translating the customer portal into multiple languages is possible with Jira Service Desk Cloud for supported languages. For Jira Service Desk Server, this functionality requires an app from our Atlassian Marketplace such as Translation for Jira Service Desk for Jira Service Desk Server.
So what I did is:
- I went to translations pages and I see that page is retiring and it will not be possible to translate for ourselves
- I tried 3rd party add on app “Translation for Jira service desk” and it is ok for some parts of your products (but not all)
- I tried your “InProduct translation for JIRA” which after installed says that it is not supported Some things work but not all
- None of below solutions work as whole
Then I found out this page https://confluence.atlassian.com/jirakb/how-to-install-custom-language-295305642.html. It says:
- Download language pack from packages.atlassian.com
- Unpack the jar file and modify the strings.
- Pack everything back into a jar file.
- Upload jar file using Jira plugin manager.
So when I try to go to packages I can download Slovenian package, which is almost empty. I wanted to download English version and start translating it to Slovenian, but English version is not available for download on translations …
To cut the long story short … I would like to have clean language pack in English language that I would like to import as Slovenian language and then start translating with apps mentioned above … al things that cant be translated this way I would like to translate by unpacking jar and adding phrases.
As I mentioned I need to only translate customer facing communication (portal, emails with links) …
For start I need to have clean language file with English words that I can rename to Slovenian language …
I hope I was clear enough 
Robert