I'm European so English is my second language and I am almost perfectly fluent when speaking to myself in English. I don't know how or why, but I can flawlessly say any word or tricky letter when I'm by myself, walking around the house, ranting. However, if I ranted to myself in Croatian, I'd almost certainly stutter. For instance, the word "Woofer"(as in Subwoofer) sounds almost the same in Croatian, but the "w" sound is not so rounded. When ranting to myself in English, I can say it no problem. When discussing woofers with my dad in Croatian, I stutter like crazy.