It is very hypocritical of Mexico to propose a construction wall along its Southern border, while they were against Trump's suggestion of building a wall along the Mexican border with US to keep of Mexican immigrants. Mexican president claim that the Southern border will keep off immigrants from Guatemala, Honduras and Salvador from reaching US is in bad faith and very hypocritical in all aspects.
Mexico's talk of a Southern Border Wall Plan is reactionary behavior and is quite honestly to be expected when US politicians have simultaneously overtaken the Mexican economy and been unsupportive of freedom of movement. To fault Mexicans for heading further north for opportunities lost at home seems like the real hypocrisy in the situation.
No, it is not hypocritical of Mexico because they are simply responding to Trump's remarks. They are showing that they will not back down from bullying. They are asserting their rights as a nation and should be praised for doing so. Trump is ruining relations between nations and should be punished for it.
Without knowing what kind of immigration issues Mexico is facing, I can't say if its plan to build a wall is hypocritical or not. It sounds like the intent is to keep out Salvadorans and Guatamalans fleeing violence, and that one issue is folks passing through on the way to the US. I don't know what kids of numbers they're getting or how disruptive it is.