Radio in Mexico is very disciplined.https://en.wikipedia.org/wiki/Amateur_radio_callsigns_of_Mexico
There are scheduled nets not only for club reasons and affairs but also to pass traffic.
Although the modern telephone is everywhere in the USA, this is not the case of Rural Mexico.
So, to simply "Jump in" a net is not only impolite, it may impede traffic.
As a rule, there is someone in the group who speaks English, but they may be very busy in the net.
I would suggest you get on the SAHARA link system when it is in use and have someone introduce you on HF.http://www.qsl.net/kd5gat/repeaters.htm
Once it is understood as to your intent, you will find a very warm welcome throughout all of the Latin Americas.
You will soon pick up the schedules and their purpose, when to rag chew and when to only listen.