The only way to get comfortable in a foreign language is to simply jump right in there and start talking.
That said, there are hazards in doing so. I don't have any equivalent stories in Spanish so far (although I sure would like to find some), but I'm going to tell you of my two favorite watch-out-for-the-language tales that occurred in Brasil.
Brasil, particularly in the northeast where this story takes place, has a very large Irish missionary presence. I've met quite a few, and they are among my favorite people. They love to tell this story on one of their own, a young woman who came over fresh from Ireland as a lay missionary about 20 years ago. She went through the standard 6 weeks training in Portuguese and then made her first trip into the interior of the northeastern state of Paraíba, where I've spent the most time.
There's a town not too far from the coast called Patos, which in Portuguese as in Spanish, means "ducks". I'm not sure why, but on this trip she was meeting with the mayor and a few other officials, escorted by other Irish missionaries, old hands in Brasil. Colleen wanted to compliment the town, so she said--she thought--to the assembled group, "You have such lovely ducks here." But instead of patos, she inadvertently came out with putas--which has the identical meaning in both Spanish and Portuguese. Her Irish colleagues had all they could do to keep from rolling on the ground, laughing, while the Brasilian dignitaries of the town did not know where to look, what to do with their hands, and certainly had no clue how to respond.
Knowing my Irish friends, I wondered about the truth of this story, but years later, I met Colleen and she laughed uproariously at the memory. Every word was true.
The other story concerns a Catholic missionary priest, an American, in João Pessoa which is the capital of Paraíba. I think it was Pentecost, and the priest, who had been there less than a year, was giving a sermon in which he wanted to say "And then the Holy Spirit descended on the disciples in the form of a dove". The word for "dove" in Portuguese is pomba. I don't remember what exactly was the unwitting change, but the priest wound up using, instead of pomba, a very similar word that was one of the slang terms for "penis". He had no idea why the older members in the congregation suddenly turned to stone or why all the teenagers were either snickering and nudging one another (male) or nearly choking from giggle fits (female).
My informant was a priest who had been there and who had enjoyed the whole thing immensely. Part of the rite of passage for missionaries, he said, refusing with a grin to tell me his own.