I have seen Translation Campaigns that requires you to put your previous works/translations. Is there any chance for a beginner, who doesn't have translations yet, to join this kind of campaigns? If yes, how? Thanks!
Just offer a free translation to any ICO so that you can have your own sample and you can start making your portfolio so that in the future you will don't have any problem when you want to join.
Well, that's a good starting point make a service for free. Or if you don't mind just try to work on something even they don't ask for. Its hard to join on that campaign if you don't have any experience but some managers are still accepting it though its very rare to find.
Offering yourself without any fee is an attracting service for those that does have a cut off budget and who doesn't want to avail a service that is for free?
You can start creating your portfolio with that way but if you insist and you can't offer a free service then look for some other interesting things or blogs or articles that you can translate.
By doing that, you can also have an additional article that you translated.
Reminder: You should translate accurately and don't depend on automated translators.