It makes the ears perk up a bit and the head turn to the side when I suggest that learning French, Spanish or any other language is going to help your English writing skills.
Dig a little deeper, and you’ll understand that a second or even third language opens up a reality that wasn’t there before. If English is your native and only spoken language, it’s something that can easily be taken for granted. The words, spelling, and meanings are what they are. After a while, you’ll understand that although you hear words that are so similar they are even spelled the same between some languages, they are used differently. Language frames how we think. French people are often described as artsy and rude. I’ve thought to myself on many occasions how rudely I’ve been treated by French people, but they have also been some of the most honest and intelligent people as well. Again, their language frames their culture and how they think, so to me they are rude, but perhaps to them I’m unclear.
Knowing another language will allow you to begin to think outside your framework. It’ll let you represent ideas that many of your unilingual readers wouldn’t have been able to frame on their own. This type of cross language / cross culture thinking could be a very good creative nugget to offer your readers.
One last thought on this, before you bury the idea. Without knowing another language, you can only really represent that type of person purely from observation. Observation is how we writers get most of our work done, but imagine you knew the language. You knew the person, framework and all. Now it’s like you’re writing from inside their head. It’s always better as a writer to try to experience something and not just see and copy.
I recommend you go out and learn another language. It’s not easy for everyone, but it’s better than chasing cars.