There's a couple ways you could go with this:

1) Use a translations / internationalization addon. You might want to check out this one:
http://www.concrete5.org/marketplace/addons/internationalization/...

2) You could create a custom template for the form block that simply renders the form in a different language. Check the documentation for more on how to do this.

Hello. Thank you very much for your answer, but my idea is simple:
I want to know in which file the word "submit" is displayed, to change it. Would it be possible?
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Auto-answer: I had just to change 'Submit' for 'Enviar' in file concrete/core/controllers/blocks/form_minisurvey.php
in the line ...<input class="formBlockSubmitButton ccm-input-button" name="Submit" type="submit" value="'.t('Enviar').'" />