I could have written this post myself. I have this experience exactly. It can be embarrassing because my stutter is a block so often it just seems like I don't know a word. People talk about achieving 'fluency' in a second language whereas I don't really feel fluent in my native language (English). The word-swap issue is so real - not just words but also rearranging whole grammatical structures etc. The only thing I can tell myself is that it took me until my mid-20s to really be able to do it well in English, so little by little I will get better at it in my L2 (Spanish). I can pass for fluent sometimes in English, so I guess spoken 'fluency' in Spanish will just take a lot longer than for people without a stutter. Of course, knowing this is a problem increases my anxiety and makes me stutter more. I have found it helps to have a range of Spanish noises/words for pausing/thinking/rewording and using these. Also just trying to chill out and remember that not being fluent is ok - someone who genuinely doesn't know the word is also allowed to speak.