Why do Orthodox crosses have those two extra bars on the top and bottom?

[FAGGOT!!!!!!!!!!!!]

And why is the bottom one slanted?

 

[baqqrih]

I believe the higher bar represents the inscription that was on the cross (the inscription saying "King of the Jews", being what the non-Jews who physically carried out the act called Him in place of the term "Messiah"), and this inscription was on a shorter, higher board than the board that they pinned His hands to. While I may not remember it correctly, the lower one, meanwhile, is the board where God's feet were, and it symbolically slants upward towards the penitent thief, who was on Christ's right. If only Spas or Aedra were still here to confirm that I'm right on this.

 

[FAGGOT!!!!!!!!!!!!]

On that note, why do Coptic and Tewahedo crosses look different, too?

Coptic Cross

Tewahedo Cross (I couldn't find a good stock image of this one so I made it myself):

 

[baqqrih]

Looking at the Coptic one, my only idea about it comes from the three-pointedness of each of its ends, which is probably representing the Trinity. Those points also add up to twelve since there are four of these three-pointed ends, so maybe then it would also represent the twelve Apostles? Even then, I've no clue why both that Ethiopian one and the Coptic one are shorter, lacking the longer bottom piece of the cross that connected it to the ground. Their crosses are probably focusing more on symbolism than crosses like the traditional, standard "Christian cross", or the Orthodox one, which go into realistic detail by having that longer piece at the bottom.

 

[centurywalker]

The thing is, according to my teacher, THAT bottom one symbolizes christ/god’s victory over sin

 

[Jimb0]

I always thought it was about the Jesus and the two thieves who were crucified with him, one accepted him and the other one mocked him

 

[Dissoziation]

I always thought it was about the Jesus and the two thieves who were crucified with him, one accepted him and the other one mocked him

Yes, it also represents the balance of justice and Christs victory over death. One side points up towards Heaven, while the other points towards Hell. I think it was historically quite common for crosses to have a footrest to prolong tortue, so its strange that the western church removed it. I guess for simplicitys sake.