So I follow the steps to marry any NPC you want, mine is Nelacar, the exiled Altmer mage living in Winterhold

1. wear the amulet of Mara
2. click on Nelacar, and check with UESPwiki to make sure it's the right id
3. setrelationshiprank player 4
4. player.setrelationshiprank player 4
5. addtofaction 19809 1 (also tried addfac 19809 1)

after this I even disable then enable him hoping the proper dialogue would come out. But sadly nothing happens, he still call me archmage, and there is no other dialogue option besides asking him why he is still living in this inn.

Why the console not working? What should I do to make it work?

I think you need to addfac 19809 1, before setting relationshipranks. It might make no difference, but give it a shot. And like Salissius said, #4 isn't needed and might actually screw things up.

Hmmm you shouldn't need step 4. I was able to successfully wed Lisette using these steps; have you tried other NPCs besides Nelacar?

The NPC needs to have access to marriage dialog. Basically, it needs the lines used by other "marry-able" NPCs. If the NPC you want uses a voice actor that never recorded those lines you will never have the marriage dialog regardless what console codes you use.

I've tried it without step 4 and with any possible sequences among step 3 to 5, and it still doesn't work. I assume it will work on other NPCs since I've read so much about this( I'll test this later) , and I can marry the official marriable NPCs. I'm wondering could it because Nelacar is a male Altmer and there's no such option in the official marriable list, that all male Altmer are unmarriable even through console?

From my own experience, a lot of the NPCs use race and gender specific voices, and only a couple of important quest-related NPCs have unique voice actors. Does this mean NPCs who have the same race and gender with the official marriable list can be married through console while others like Bosmer or male Altmer or those with a unique voice can't? I'm not sure if Elisif the Fair has a unique voice actor, but I do see someone successfully marry her(even she is listed as "NPCs the Player cannot marry" in UESP).

I'm wondering if someone has successfully married Elenwen( the Thalmor ambassador), she has a unique voice and there's a female Altmer option on the official list.

And I'm not sure if I've made myself understood...

Try the SetMarry Mod on Skyrim Nexus. I just went and married the beatiful bard girl of ivarstead. This was after divorce from Lydia which works with another Mod^^

Funny Thing is. all the Dialogue after the marriage is normal, no bugs so far. Shes now living in my House in Solitude. Really whonder why you cant marry those Npc′s in the First Place.

I think some of them are still predisposed to marry certain factions. I tried thecode on a bunch of people, including a few on the marriage eligible list and they still wouldnt give me the option to marry them. So I dont think that code is quite as useful as it is made out to be. I would say at best if an NPC likes you enough or is neutral enough then using the code will give them the dialogue option but I dont think it just opens it up for everyone. I have tried bothLydia and Ysolda on my Imperial (gone all the way through civil war storyline) and neither will give me the option, just like they wouldnt before i used the code. I have tried every name on the list and basically only 3 of them gave me the option before I tried the code. I havent tried many since i got the code, but I doubt I gain more than a few names, if any, eventhough theyre supposed to be options without it. I am going to try Ria next, she is an imperial and without the code she doesnt offer me anything. Will try the code and see if it unlocks it, but I doubt it, but that guy is bugged on the companions quest so not sure, similar to Aela, but I auto completed it to ask them both last time (then reloaded the save when they wouldnt) so not sure if that bugs it out or not.

You have a link for that? Searching SetMarry and Marry didn't find it on Nexus.

EDIT: Found it. Odd mod since it makes you use the console anyway. If I'm going to do that then I don't need a mod to begin with.