Is it permissible to call someone named Zakaria by "Zaki," or someone named Abdullah or Abdul Karim by "Abdou," keeping in mind that the Algerian dialect adds the elongation "ou" when referring to the pronoun "he"?

There is no objection to calling a person by an altered version of their name, whether abbreviated, lightened, or softened, so long as it does not cause them harm. This is following the example of the Prophet (peace and blessings be upon him), who called Aisha "Ya A'ish," Abu Hurayrah "Abi Hur," and Uthman ibn Affan "Uthm." However, changing a name out of contempt is not permissible, due to the Almighty's saying: "And do not defame one another, nor call each other by offensive nicknames. Wretched is the name of disobedience after faith."