Hello all,
I am new, so please excuse me if this is not the right place to make this suggestion.
My idea is the following: why not let everyone, without applying, be able to sub trailers? These are short videos that often lack subtitles in languages that are not so common on Viki. Being able to sub them would help rookies gain valuable experience. 
Subbing trailers can also help a rookie’s application to a project, as it shows interest and commitment.
What do you think? 
Many years ago, way before I joined Viki, all shows were fully open to work on by everyone. You can imagine that that lead to chaos, inconsistency and at times, fraud.
So Viki developed designated channels that you could only work on if you were part of the team. Initially, everyone could be added, but later on, we got restrictions for being added as a language moderator. This was mainly done to make sure that all moderators had experience and didn’t take on too many projects at the same time.
Now, we can only give someone access to a trailer if we add them to the team and that would mean they had access to the entire show. Not ideal if trust still needs to be build.
Also, the moderator of each language is responsible for the subtitles for that show in their language and they need to be consistent. They can’t have people that are not in their team suddenly work on their trailers.
And this is why in recent years, Viki came up with sample videos for newbies. First only in Spanish and Portuguese, but nowadays they are available for starters in all languages.
Apart from that, apply directly to the moderator of your show of choice, write the application in the language you want to sub in and make sure you don’t have any typos or weird errors.
I saw you already found a Bulgarian moderator so for now, you should be fine. 
Thank you very much for the detailed explanation, this was very helpful.