This community seems distrustful of, uhm, aliens. It can be seen the forum's statistics: there are two distinct groups of users, those who come here for quite short time and never come back, and everyone else. The latter eventually become hero and legendary users, and the former remain foreigners forever.
Is there any way for newbies to build reputation besides spending months to become a regular? Maybe some kind of a guarantee given by an already reputable user?
There is no shortcut. Share your wisdom with us and if you are wise enough the community will reward you for sharing your wisdom. Build stuff, make translations, share market predictions... Share something which not many people are aware of. Sometimes even sharing basic news attracts merits. You will never know what works the best unless you try and even then, you shouldn't be doing it to get merits and rank up fast, you should be doing it because you like to do it. I see many people went from newbie to hero quickly and they mostly did what I just told you.