Apologies for not being too clear on my previous post.
English proficiency is certainly a vital requirement for international aviation to work. However if for whatever reason I can't attend to a scheduled exam and instead would have to wait for the next one... say a week later and months before my current rating expired, I COULD be charged within the current legal framework.
Here is a link to the current law (spanish, sorry).
On all the towers that were privatized the controllers got letters informing them that they had to "voluntarily" request the OJTI rating or risk being charged with "obstructing provider change" as stated on that law.
As said before, the information is available to the general public, read it and decide if you really need that job so badly.