I'm not nearly as articulate as Lahiri, nor does my profession allow me to dive so deeply into language issues. But as I muck through learning Mandarin, I find myself feeling similar frustrations and experiencing similar exhilarations.
Let me start by saying I am painfully bad at Chinese. My audio lessons ask me to say something and then pause for me to say it, and I almost never know how to say it, and even if I do I can't do it in the time given. Why? Because I have to figure out what order the words go in (because Mandarin grammar is different from English), then I have to remember how to say each word, and if that wasn't bad enough Mandarin is tonal so I have to remember what inflection to give each word. By the time my puny brain has processed all that, my audio lessons are already onto the next sentence. Dur!
Having once spoken Taiwanese, and having taken a year of Mandarin in college, I have something to work from when it comes to decoding grammar. And, I have a base of words that I no longer have to translate from English but I just "know" as being those things (recall my clunky example a while back about "cat").
But other words are brand new to me, and I have to figure out how to remember them, and I often do not. If I had time I would enlist human help, because that feedback loop would be useful, but my Mandarin is so primitive and slow right now that even simple conversations would be arduous exercises. I hope to get there in a few months.
So it's a lot of slogging and a lot of "I forget" and a lot of "I didn't say it right." Which is a healthy thing for this Type A person to experience. As are some small victories of recognition and good pronunciation. Lahiri's relationship with Italian is beautiful, while mine with Mandarin is far patchier. But it is a thing in my life, and it adds texture to my life, and for that I am grateful. And one day I will be able to have a conversation with someone in a language besides English, and that will be really fun.