"Yo le hablo a la mesera en francés."
Translation:I speak to the waitress in French.
Apparently, there are several Spanish verbs that require a redundant indirect object pronoun even when the indirect object is also in the sentence. I'm still looking for a complete list but verbs of communication like hablar and decir are included.
Elizadeux, I don't think it is a question of certain verbs requiring redundancy and others not. My understanding is that if there is an indirect object (to whom or for whom an action was done) in a sentence, there must be an indirect object pronoun used, not just for specific verbs, even with redundancy. As per http://www.spanishdict.com/answers/100017/indirect-object-pronouns#.W37Z8dJKi01 : "When to Use the Indirect Object Pronoun: If there is an indirect object in a sentence, there MUST be an indirect object pronoun! You can also have the prepositional phrase "para nosotros" or "a Miguel" to add emphasis, but you can NOT only have the prepositional phrase."
That said, to expand on what kennypi shares, communication verbs provide a grey area as there can be an ASSUMED direct object (what is being communicated) and in that case you CAN use an indirect object pronoun to refer to the person the "thing" is being communicated to (as in the example sentence), but it isn't required.
Hablar and decir commonly use an indirect object pronoun, but these verbs do not require one.
In American English there is a movement towards using "waiter" for either gender, so "I speak to the waiter in French" should be an acceptable translation.