Sorry, I will answer in English to this one because I think it's really an important problem.
If you see an abandoned project in your own language:
Contact your language's moderator on that project and ask if she/he would put you up as a subtitler to finish the project.
If the moderator does not respond after 2 tries within two weeks, contact the channel manager or English language editors to be put either as a subititler or moderator for your language. (Note: only persons with enough experience in subtitling can become moderators.)
If none of the persons above respond after two emails, send a request to the Viki directly by following this link:
Choose category Subtitling Tools, since it's the closest to the problem you have.
If the language moderator rejects your offer and there has been no activity on the project in the last for example 6 months, contact the CM of the project. Moderators should be accountable to finish their own projects.