Add a Mexican Spanish Translation

[TheLegendofSaram]

I know there is a es_es file already, but its lacking most of the lines and its using a very localiced spanish, european spanish, this is a more "globaliced" spanish, it can be used as a es_mx, es_ar, es_cl, es_ve, and even es_es. And I already know that the translation is uploaded thru crowdin, but it wont let me add a es_mx variant