I know the letter is a bit long so Thanks a lot for your time !!
Here we go :

I am currently enrolled in a Master of political Science in XXX. Part of my course implies the completion of an internship starting anytime from July. Through this internship I want to achieve two main goals:
1. Working in the research and development department of a well established NGO to gain hand on experience and pursue my career in this field.
2. Working in Brazil as I highly desire to develop my understanding of Portuguese and would like to have experience of the country.
If my proficiency in Portuguese is still basic I nonetheless have an excellent understanding (written and oral) of Spanish that allows me to well read and understand documents in Portuguese. I am also strongly driven in pursuing my efforts in learning this language.
{which formulation is best ?}
1) I am convinced that I display assets that would benefit to XXX if I was assigned to support the “Name of a person”.
2) I am convinced that I display assets that would make me be a productive member for XXX in the quality of subordinate to “Name of the person”.
Besides my working experience and my academic records, my excellent understanding of French and English allows me to contribute immediately to two aspects of this role:
1. Collection and production of materials about the reconstruction of Haiti. Analysis of government proposals.
2. Develop and maintain contacts with overseas partners and organizations.

Moreover, to complete my Master I undertook the writing of a thesis, which is due to December this year. I have chosen to work on the humanitarian response to the Haitian crisis and the post-crisis management. This means that I will dedicate my personal time gathering and analysing data on the matter therefore providing "The organization name" with substantial extra materials.
Furthermore, as I will progress in my understanding of Portuguese I will steadily be able to assist in the support of the regional and national programs of "Name of the organization" or any other requested task.

Finally, in case of a positive response, I will make arrangements to come to Brazil as soon as possible (beginning of June) to undertake intensive Portuguese classes.

Madam, Sir please be ensured of my high commitment and enthusiasm regarding the above proposal.
If you have the possibility, I would appreciate if you could confirm good reception of this email. In any case, I will contact ActionAid Brazil office in the course of next week to discuss the matter further.

Yours sincerely,

Thanks again for the courageous that have read the letter till the end
Any comment welcome !