Hello Pablo Tola,
You have most probably referenced the en-us dictionary also. When it is referenced and the current thread culture is set to en-us also, then the en-us dictionary takes precedence over the invariant culture one. What is recommended in your case is to add the dictionary to the es-ES culture instead of the invariant one and change the current thread culture to es-ES. This will ensure a correct behavior. For example:
Don't hesitate to contact us if you have other questions.
the Telerik team
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